Browsing by Author "Knutsen, Robert"

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    Open Access
    A study on the effect of increased heat input on residual stress, microstructure evolution and mechanical properties in Ti6Al4V selective laser melting
    (2021) Motibane, Londiwe Portia; Knutsen, Robert
    The Aeroswift machine is a novel high-speed powder bed fusion machine developed through a collaborative effort between the CSIR, Aerosud and the DSI. Its novelty lies in the substantial increase in build rate achieved through the implementation of a 5kW IPG laser and faster laser scanning speeds employed during processing. It is capable of producing Ti6Al4V low volume, high value and high integrity components required by the aerospace industry. Commercial selective laser melting (SLM) systems are a good benchmark for the type of quality needed in the integrity of aerospace components although they don't always meet them. The biggest difference between commercial systems and the Aeroswift machine is the amount of heat input used to make components based on the laser powers. Heat input is the ratio of the laser power to the scanning speed and it plays a role in the thermal history of a built part, its thermal gradients and therefore its residual stress. Heat input also has a big influence on the microstructure produced which determines the resultant mechanical properties. The focus of this project was to investigate the effect of increased heat input on residual stress, the development of microstructure and mechanical properties of Ti6Al4V specimens produced by the Aeroswift high (400 J/m) heat input system and commercial SLM Solution M280 low (150 J/m) heat input machine. This was to be accomplished by comparing the tested results of Aeroswift built specimens (High Heat Input) to those built by a commercial SLM machine (Low Heat Input). The effect of preheating on these properties was also studied. The low heat input specimens had two sets of test specimens, where one set was built without preheating and the other built at a preheating temperature of 200°C. This was the maximum preheating temperature for the commercial system used in this study. Firstly, the cantilever specimen were used to measure the amount of distortions that processing caused for both systems. The measured spread of the cantilever gave an indication of the amount of distortion caused by each processing condition. Distortion was found to be similar between the high heat specimen and the low heat specimen. Preheating at 200°C also did not give an appreciable difference in the amount of distortion. X-ray Diffraction was used to measure very near surface residual stresses up to a penetration depth of 5 microns. Blocks of 20X20X22 mm3 for each processing condition were used with measurements taken at the top surface center of the blocks. The very near surface stresses were higher with an increase in heat input, where high heat input specimens had average tensile residual stress in excess of 650 MPa while the low heat input specimens had average tensile residual stresses below 400 MPa. The Incremental hole drilling technique was utilised to measure the stresses in the blocks up to a depth of 1 mm from the top surface. Holes were drilled at the top surface center of each block. The stress distribution for both the high heat input specimens and the low heat specimens increased from 0.2 mm to a similar range of 500-600 MPa between 0.3 mm to 0.8 mm depth. Preheating at 200 °C yielded the same amount of stress. The microstructural analysis involved imaging from Optical Microscopy, Scanning Electron Microscopy and Electron Backscattered Diffraction. This combination of techniques confirmed a martensitic microstructure morphology of α' laths within prior β grains for all the specimens. The α' laths were arranged in the form of basket-weaves as well as colonies. The high heat input specimen prior β grains were columnar having grown across several layers in the build direction. For the low heat input specimens both with no preheating and with 200°C preheating, the prior β grains were atypically discontinuous. A hexagonal-titanium phase was identified in all the specimens as the dominant phase, with essentially no presence of the cubic phase. Dog-bone tensile specimens built in the z-direction (build direction) were used to test for static mechanical properties. The Yield Strength and the Ultimate Tensile Strength were above 1000 MPa and 1200 MPa respectively for all specimens. The average elongation of 11.2% in the low heat input specimen with no preheating was significantly higher than the 4.3% achieved by the high heat input specimen. The effect of the observed micro porosity under the microscope is thought to have contributed to this behaviour. Compact tension specimens for fracture toughness and fatigue crack growth rate testing were built in the ZX direction as per ASTM E399-17 labelling. The high heat input specimens had an average fracture toughness of 43 MPa√m compared to the less than 38 MPa√m achieved by the low heat input specimens. The high heat input specimens also had a better crack growth resistance than the low heat input specimens. The low heat input specimens without preheating had better crack initiation resistance. The results show that an increase in heat input does not have a substantial effect on the integrity and quality of parts. In fact, it produces comparable results to commercial SLM processing deployed in this study with respect to the properties studied, with the exception of a lower ductility. This brings about even more confidence on the advantage of high-speed processing. Future work should include testing at other orientations as well as testing higher preheating temperatures.
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    Open Access
    Homogenisation of titanium - 6 aluminium - 4 vanadium (TI-6AL-4V) powder blends during sintering
    (2022) Churu, Varaidzo Amanda; Knutsen, Robert
    Titanium alloys have received significant attention in recent years primarily within the aerospace sector due to their superior material properties, high strength to weight ratios and high resistance to corrosion. However, high processing costs associated with the alloys have hindered their usage in other fields such as the automotive industry. The powder metallurgy (PM) method is an emerged method that may lower processing costs. The blended elemental (BE) route to produce titanium alloys has been identified as the cheapest process by which the PM process can be applied. The powder metallurgy method has a few limitations, one of the associated limitations is that elemental powder blends must be homogenized in terms of chemical composition for them to meet the same quality standards as ingot processed titanium alloys. To combine cost effectiveness with good mechanical property attainment, the sintering process should be optimized at the lowest temperatures and shortest duration. In the current study, Ti-6Al-4V alloys were synthesized by the blended elemental press and sinter powder metallurgy route. This was carried out using three different powder blends comprising of Ti (100µm) and TiH2 (63µm) as base powders, blended with either Al (75µm), V (25 µm) or a 60Al-40V (40µm) master alloy powder (MA). The powder blends made from the powders were namely TiH2 + MA, TiH2 + Al+ V and CpTi + MA. The average particle sizes in each case are indicated in parentheses. As a precursor to mechanical property measurement, the relative degree of homogenization that occurs during sintering of powders shaped by uniaxial pressing was investigated at sintering temperatures of 1000 - 1350⁰C under vacuum at times ranging from 0.5 hours to 4 hours. The homogenization was evaluated via scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDS) and X-ray diffraction (XRD). The density was measured using the Archimedes method. The EDS approach was used at a specific length scale (100µm× 100µm) to assess the degree of elemental mixing that occurs during the limited sintering exposure. A combination of SEM/EDS analysis and XRD was successfully used to measure homogenization progress of the powder blends. The different powder blends reached different levels of homogeneity at different temperature and time. The TiH2 + MA powder blend became fully homogeneous after sintering at 1350°C for 2 hours with a relative density of 98% ± 1. Three stable beta peaks coinciding with the wrought titanium spectra were also shown after sintering at 1350°C for 2 hours . The CpTi + MA powder did not reach full homogeneity as the TiH2 + MA powder blend at any of the sintering temperature and times but after sintering at 1350°C for 4 hours the samples demonstrated reasonable homogeneity, although still significantly less homogeneous than the wrought alloy. There were some peaks that had peak broadening and peak splitting also shown that were closely related to the beta peaks of the wrought titanium shown in the XRD spectra but were not fully stable and a relative density of 97% ±1. The TiH2 + Al + V powder blend also did not reach homogeneity at any of the sintering temperature and time, there was however an improvement in diffusivity of aluminium and vanadium after sintering at 1350°C for 4 hours, with a relative density of 96% ± 1, no beta peaks were shown in the XRD spectra. The factors that mainly affected homogeneity besides time and temperature were the type of base powder as well as alloying elements. From the experiments, it was noticed that when Al and V are added as elemental alloys there was a 2-hour increase in sintering time for relative homogeneity to improve due to aluminum diffusing faster than vanadium at lower temperatures and stabilizing the alpha titanium phase. Whereas when vanadium and aluminum were added as a master alloy it resulted in a faster diffusion of both elements, therefore, reaching homogeneity earlier. The combination of TiH2 + MA powder blend had the lowest temperature and time reaching homogeneity at 1350°C after 2 hours of sintering.
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    Open Access
    Influence of laser scan rate on the mechanical properties of SLM TI6AL4V alloy
    (2022) Matjelo, Lehlomela; Knutsen, Robert
    The influence of laser scan speed on the resulting axial tensile, fracture toughness and fatigue crack growth rate (FCGR) properties has been investigated on samples produced by the selective laser melting (SLM) process from a Grade 5 Ti6Al4V metal powder; the laser scan speed was varied from 1.5 m/s to 4 m/s, while other process parameters were kept constant. Test procedures and specimens were designed in accordance with the ASTM E8/E8M, ASTM E399 and ASTM E647 standards and the corresponding microstructural characterisation carried out using optical microscopy in bright field mode. The bulk densities were investigated in line with ASTM B962-15 (Standard test method for density of compacted or sintered powder metallurgy (PM) products, using Archimedes' principle) and varied from 96% to near-100%. The ultimate tensile strength (UTS) for the as-built SLM Ti6Al4V uniaxial tensile specimens ranged from 1007 MPa to 1333 MPa, with the total elongation at failure (ductility) ranging from 4% to 9%. Nevertheless, there was generally very poor correlation between scan rate, density and measured mechanical properties. Consequently, it was proposed that the form and distribution of porosity would be more likely suited to explaining the mechanical property data. This led to a second batch of samples being produced at 3 m/s and 4 m/s for the sole purpose of investigating the influence of pores on the mechanical properties for the now stress-relieved (650°C for 4 hours in vacuum, furnace cooled) SLM Ti6Al4V samples. The uniaxial tensile test, fracture toughness test and the 3-point bend fatigue crack initiation test results were studied in conjunction with the X-ray computed tomography scans (X-ray CT scans), which were done prior to testing, and fractography carried out using the secondary scanning electron microscope (SEM) images. The UTS for the stress-relieved SLM Ti6Al4V dropped to a range of 1000 MPa – 1120 MPa, while the ductility for samples fabricated at 3 m/s was improved (7±3% to 12±2). Comparison across the 3-point bend fatigue test results for specimens fabricated at 3 m/s and 4 m/s indicated highly variable resistance to crack initiation. The results and analysis for the as-built and stress-relieved SLM Ti6Al4V mechanical test specimens led to the conclusion that the scattered mechanical measurements observed in this project could be attributed to variable porosity in samples, which overshadowed any correlation to be made between the laser scan speed and the measured mechanical properties; severe porosity in mechanical specimens played a major role in their mechanical response.
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    Open Access
    Influence of post-weld heat treatment (PWHT) on the tensile behaviour of P91 weldments
    (2023) Jambo, Tinashe; Knutsen, Robert
    A key factor for successful installation of Grade 91 steel for high pressure-high temperature applications in power plant is optimised welding and post weld heat treatment (PWHT) which restores homogeneous mechanical properties after welding. Although optimum PWHT is prescribed in standards, deviations in the field practices can potentially lead to accelerated component degradation and failure. Consequently, a full understanding of cross-weld behaviour as a function of deviations in PWHT is required. This study investigates the influence of PWHT on the occurrence of strain localisation in cross-weld tensile specimens tested at temperatures up to typical power plant service temperature. Localised strain maps were obtained during high temperature tensile deformation. These assist in understanding the influence of PWHT on the overall performance of the cross-weld, and the identification of the location most susceptible to failure in the welded specimens. Specimens used in this work were extracted from as-welded new Grade 91 pipe material. Wire cut EDM was used to extract rectangular blocks with the weld in the centre which were machined to required geometry. Specimens for as-welded (AW) tests were not subjected to PWHT. The recommended PWHT for P91 steel is tempering at 760°C for 2 hours. Post weld heat treatments that were performed on specimens included soaking at 720°C, 760°C and 800°C for 2 hours respectively, as well as so-called excursion heat treatments that included extended treatment at 760°C for up to 6 hours. In addition, excursion heat treatments also included over-heating up to 840°C followed by soaking for 2 hours at 760°C. A Gleeble 3800D thermomechanical simulator was used for high temperature tensile testing at a strain rate of 103 s-1 . High temperature tensile tests were performed at 300°C and 535°C. Three-dimensional (3D) digital image correlation (DIC) was used for non-contact strain measurement (i.e., application of virtual strain gauges) to accurately map the occurrence of strain localisation. DANTEC Istra 3D DIC software was used for capturing and post processing the DIC data for strain analysis across the weldment. Specimen subjected to PWHT exhibited reduced resistance to deformation at room temperature having a lower yield strength (YS) and ultimate tensile strength (UTS) compared to the AW condition, indicating that PWHT lowers the materials resistance to the onset of plastic deformation. Despite an overall reduction of UTS at elevated temperatures, this observation was extended to tensile strength at elevated test temperatures. Over tempering resulted in diminished tensile properties as observed in specimens tempered at 800°C for 2 hours. A comparison of specimens subjected to excursions and extended heat treatments shows that excursions resulted in poor tensile properties, exhibiting very low yield strength and ultimate tensile strength compared to the recommended PWHT. Specimens subjected to excursions and over tempering in PWHT exhibited diminished tensile properties compared to the recommended PWHT. The change of tensile behaviour across weldments as a function of PWHT contributes to understanding the metallurgical risk associated with deviations in PWHT field practices. Localised strain maps showed that the weld metal has high resistance to deformation at room temperature which decreases as test temperature increases. At room temperature the peak localised strain occurred in the base metal (BM) for all PWHT conditions. The peak localised strain migrated further into the BM with increased PWHT temperature, while it occurred in a hot zone at elevated test temperatures. Based on experimental results obtained at room temperature, strain localisation was established as a function of heat treatment condition. The non-uniform temperature profile remains a challenge to reliably conclude the extent to which strain localisation is influenced by heat treatment and material property.
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    Open Access
    Investigation of the stress corrosion cracking resistance of SAF2205 and AISI304 weldments for the marine environment application
    (2021) Matjee, Mapula Regina; Knutsen, Robert
    Stainless steels are used for many industrial applications because of their strength and fabrication characteristics. Stainless steel grades of SAF2205 and AISI304 can readily meet a wide range of design criteria of service life, maintenance, load and corrosion resistance.
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    Open Access
    Mechanical property and meso-structure assessment of Ti6Al4V parts as a function of high-speed selective laser melting practice (Additive Manufacturing)
    (2022) Nyakunu, Chenesai; Knutsen, Robert
    The use of titanium and titanium alloys, particularly titanium-6-aluminium-4-vanadium (Ti6Al4V), manufactured by 3D printing, also known as additive manufacturing, is fast evolving in several industries including the aerospace industry, medical industry, and the automotive industry. At present, titanium parts fabricated by additive manufacturing techniques such as the selective laser melting practice are built at conventional laser scan speeds typically between 0.1 m/s and 1 m/s. This project is focused on investigating the influence of high laser scan speeds on the microstructure and mechanical properties of Ti6Al4V fabricated by the selective laser melting technique. Building material at much higher scan speeds allows for a higher rate of productivity and efficiency as more parts can be built in a shorter space of time. The aim of this project is to ensure that the integrity and mechanical behaviour of the Ti6Al4V parts at the high scan speeds is still maintained by investigating whether acceptable mechanical properties are still achieved when material is built at higher scan speeds. The material tested in this project was built by the selective laser melting (SLM) technique at four different high scan speeds namely 5.75 m/s, 6.0 m/s, 6.25 m/s and 6.5 m/s. The material for mechanical testing consisted of tensile specimens and compact-tension (CT) specimens for fracture toughness (FT) testing and fatigue crack growth rate (FCGR) testing respectively. The same material was used for microstructure analysis. Furthermore, the tensile specimens were fabricated in different build orientations namely X-TA, Y-TA, and Z-TA to investigate the effect of build orientation on tensile properties. During the SLM process, considerable thermal related stresses develop in the material being built. After fabrication, a heat treatment protocol was therefore applied to the material for stress relief. The material was heated at 600°C for two hours then cooled in air. Tensile testing was performed on the SLM Ti6Al4V built tensile bars according to the ASTM E8/E8M standard on the Zwick machine at a strain rate of 10-3 /s in conjunction with a video extensometer for more accurate results. Specimens were loaded in tension with force of approximately 20 000N. The results indicated that there is no significant influence of high scan speed on the tensile properties of the material tested as there was no difference observed in tensile properties of the material built at the four different high scan speeds. The same phenomenon was observed with build orientation. The tensile properties of the specimens built in the horizontal direction (X-TA and Y-TA) and the specimens built in the vertical direction (Z-TA) were within the same range. The FCGR and FT tests were performed on the ESH servo hydraulic fatigue machine at room temperature according to the ASTM E647-15 and E399 standards, respectively. The FCGR tests were conducted at a load range of 1.3kN and stress ratio of 0.1. The results indicated that there is no difference in FCGR behaviour with respect to scan speed between the 5.75 m/s and 6.0 m/s specimens as one set and no difference between the 6.25 m/s and 6.5 m/s specimens as the other set, but a difference is observed between the two sets of speeds. All specimens however, displayed reasonable resistance to crack growth. The FT tests were performed at a crosshead speed of 1 mm/min. The results indicated that high scan speed has no significant influence on the fracture toughness of SLM Ti6Al4V material as there was no difference observed in fracture toughness of the materials with increase in scan speed. The techniques used for microstructure analysis were light microscopy and scanning electron microscopy (SEM). Light microscopy was performed to reveal the microstructure and surface topography of the material built at the four different high scan speeds and three different build orientations. The results indicated that high scan speed has no significant influence on the microstructure of the material investigated. The results also indicated that build orientation influences the microstructure of the material tested. A difference in microstructure, particularly the orientation of β-grains, was observed with build orientation. The X-TA and Y-TA specimens have β-grains aligned more perpendicular to the tensile axis whilst the Z-TA specimens have the β-grains aligned more parallel to the tensile axis. However, this difference in β-grain orientation did not influence the tensile properties of these specimens to a greater extent. SEM was performed to obtain quantitative information on microstructure, particularly porosity, and for β-grain reconstruction by electron backscatter diffraction (EBSD) for the material at a much higher magnification and depth of field. The results indicated that high scan speed has no influence on porosity of the material tested as no difference was observed in the number and size of pores amongst the samples built at the four high scan speeds. However, average relative density of 97-99% was reported for these specimens which is lower in comparison with average relative density of >99% reported for the majority of the specimens built at conventional scan speeds. EBSD analysis shows that there is no difference in the size and morphology of reconstructed β-grains across the material built at the high scan speed. It is concluded that there is no significant influence of high scan speed on the microstructure and mechanical properties of SLM Ti6Al4V within the scan speed range of 5.75 m/s to 6.5 m/s investigated in this project. The specimens built at the specified scan speeds have similar energy density input which attributes to the similar microstructure and mechanical behaviour of the specimens observed.
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    Oxidation kinetics of 316l stainless steel in the pressurised water reactor environment
    (2019) Matthews, Ryan Paul; Knutsen, Robert
    With a view to improving the prediction of primary water stress corrosion cracking in austenitic stainless steels, this investigation measured the oxide growth kinetics of 316L stainless steel when exposed to a simulated primary water environment of a pressurised water reactor (PWR). It is generally accepted that intergranular oxidation at the surface of a metal forms a preferential site for stress corrosion crack (SCC) initiation; therefore the kinetics of both surface and intergranular oxidation were measured. The influence of temperature, within the range of PWR primary water (290°C, 320°C and 360°C), as well as the influence of starting condition (annealed, 20% elongated, 30% elongated and 20% cold rolled) was investigated. Samples were prepared with the various starting conditions and exposed to simulated primary water, at the specified temperatures, for various durations from 1 hour through to several thousand hours to plot the oxide growth on a log scale time axis. Subsequent to the exposure tests, the Cr rich inner oxide depth was measured locally at selected locations. The surface and intergranular oxide depth was directly measured from cross-sections either with a transmission electron microscope for short duration exposures or, for longer exposures with deeper oxides, within a scanning electron microscope. No significant difference was noted on the oxide kinetics between the various starting conditions evaluated. Temperature, however, had a significant influence with oxide growth kinetics decreasing, rather counter-intuitively, as temperature increased through the measured range. In addition a strong dependency on grain orientation was observed. A modification to the Point Defect Model was proposed to arrive at a quantitative expression to describe surface and intergranular inner oxide growth as a function of temperature in 316L stainless steel, which accommodated the deviation from Arrhenius behaviour through the measured temperature range. Functions for both the rate constant, ��3 0 , and the transfer coefficient, α3, associated with the metal/oxide interface reactions were developed. The resultant model was able to predict, with reasonable accuracy, the growth of the Cr-rich inner oxide over time. The most consistent explanation for the deviation from Arrhenius behaviour was that the coherency across the metal/oxide interface degraded as the temperature increased through the tested temperature range. This would reduce the potential for ionic transfer across the interface necessary for the interface to migrate and increase the oxide depth. Since a similar temperature dependence on the growth of intergranular stress corrosion cracking (IGSCC) in the primary water environment has been observed within the same temperature range, it is proposed that the above explanation, observed in the absence of applied stress, extends to explain the behaviour of IGSCC kinetics in austenitic stainless steel.
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    Parametric study on the compactibility of Ti-6Al-4V during direct powder rolling
    (2019) Naicker, Hiranya; Knutsen, Robert
    The widespread use of titanium and its alloys in structural applications has been limited to few highend applications. The dominant reason for this being cost implications. These high costs arise from extracting titanium from its mineral form as well as that of the manufacturing processes to develop a final product. Since producing titanium products includes expensive starting stock, high machinability costs and high wastage, a need for a process that may minimize one or more of these factors is necessary. One such technology that exists is a branch of powder metallurgy (PM), direct powder rolling (DPR) which allows for a continuous approach to produce strip or sheet metal. Products developed by this process are however known to possess inferior properties to its wrought counterpart. The present study comprises of a parametric study observing how two different blends of powder differ in the development of Ti-6Al-4V strip by employing the blended elemental (BE) approach to direct powder rolling. The objectives of this work include predicting the compaction behavior of the two respective blends during powder rolling to inform the production of high density green strip and to compare the outcomes of the prediction method to experimentally determined results using a gravity-fed laboratory-scale rolling mill with roll diameter of 265 mm and roll width of 150 mm. Johanson’s rolling theory was applied to predict rolling outcomes and a fixed set of rolling parameters were implemented for the simulation and experimental segment of this dissertation. The two blends being investigated include blending titanium powder with an elemental blend consisting of aluminium and vanadium powders (B1) and a master alloy blend of a 60Al-40V master alloy (B2). These two blends were used to validate the Johanson simulated rolling data. Fixed parameters applied to the rolling mill included using a roll speed of 14 rpm, roll face width of 65 mm and gravity-fed hopper outlet diameter of 25 mm. Variable roll gaps of 0.5, 1 and 1.5 mm were studied. Average relative green densities of B1 and B2 strips achieved at a roll gap of 1 mm were 77% and 73% respectively. Rolling performance of the B1 powder blend were higher than that of B2, reaching higher green densities and showing superior formability, as rolling at smaller roll gaps was achievable for B1 and not B2. Green strength of B1 and B2 strips at a roll gap of 1 mm reflected similar outcomes where B1 strips required a greater breaking load to fracture samples when compared to B2 indicating a stronger self-supporting compact. Furthermore, the Johanson rolling model proved to overestimate reasonable roll pressure values, although, the general trend of compactibility between B1 and B2 powder blends was reasonably predicted showing B1 to be more compressible than B2 during powder rolling. iv Subsequent sintering at 1200 °C for 3 hours in a vacuum environment was applied to green strips to further densify and homogenize strips. Average relative sintered densities achieved for B1 and B2 strips rolled at a roll gap of 1 mm were 78% and 87% respectively. While green densities of B1 strips were higher than that of B2 strips, it was evident that the addition of the 60Al-40V master alloy to blend B2 resulted in superior sinterability as final sintered densities surpassed that of B1, even when starting at a lower green density after rolling. SEM/EDX was used to evaluate what effect sintering had on homogenization. A standard wrought Ti-6Al-4V specimen was used as the benchmark to compare homogenization results. B2 strips homogenized more than B1 strips when comparing to the baseline wrought sample. It was concluded that both B1 and B2 powders used to create Ti-6Al-4V strip by direct powder rolling (DPR) exhibited high levels of porosity and a subsequent step is necessary to fully densify the material. While B1 strips exhibit superior rollability with higher green densities and green strength; after applying a sintering practice to both B1 and B2 strips, B2 sintered densities surpassed those of B1 and prove to homogenize to a greater degree than B1 strips. The superior roll compaction ability and inferior sinterability for B1 powders was attributed to the elemental powder, aluminium. While the addition of ductile aluminium to B1 aids roll compaction, its low melting point results in large pores evolving at sintering temperatures almost twice its melting point.
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    The development of an experimental technique to measure the influence of temperature on the mechanical properties of weldments
    (2018) Singh, Kashir; Knutsen, Robert
    In large industries, such as in power stations, welds are widely employed to join different components together to meet various property requirements. The thermal gradient that develops during welding causes an inhomogeneous distribution of material properties, in areas adjacent to the weld, known as the Heat Affected Zones (HAZ). Welded joints subjected to elevated temperatures and loads during operations often experience a degradation of mechanical properties and performance of the joint. Studies have found that mechanical phenomena’s such as, fatigue and creep have compromised the structural integrity of weld zones. In essence a welded component acts as a composite material, for which it’s overall performance is dependent on its weakest material component. This study focuses on developing an experimental technique that is capable of measuring the influence of temperature on the mechanical and material properties across a weldment. The development of the experimental technique includes the design and optimisation of the hot zone of a welded tensile specimen, identification and characterisation of the different weld zones as well as, refining a strain recording strategy to detect the localised strains in each of the different weld zones. The application of the experimental technique is applied to welded components from turbine steam penetrations, which were extracted from a coal fired power station. The steam penetrations are a low Cr structural steel; (Cr 0.66, C 0.24 by wt. %) and have been in service for approximately 24 year (± 212 000 hrs). Two primary systems namely the Gleeble 3800 thermo-mechanical simulator and digital image correlation are used in this study. In order to accurately map the in-service evolution of material properties, each of the welds were mechanically loaded in tension and exposed to elevated operating temperatures. To induce mechanical loading at constant elevated temperatures, a Gleeble 3800 thermo-mechanical simulator with a tensile module was used to deform specimens at a strain rate of 50 µε.s1 . Experiments were conducted at various temperatures, ranging from room temperature (RT) to 535 o C. The evolution of material properties across the weldment was evaluated using Digital Image Correlation (DIC). DIC is a non-contact digital technique, capable of measuring localized strain during mechanical loading at elevated temperatures. In order to investigate the localized strain across the different weld zones, virtual strain gauges of one millimetre in length were simulated at intervals of one millimetre. It was found that there was a continuous accumulation of strain from the Fusion Line (FL) into the Parent Material (PM). This finding suggested that the HAZ nearest to the PM; which was the Fine Grained Heat Affected Zone (FGHAZ) was the weakest zone as it strained the most. The FL was found to be the least ductile region of the weld as most of the absorbed thermal energy provided during the welding process was used for strain hardening. At elevated temperatures, localised strain occurred at lower strain values than those at RT. This finding suggested that at elevated temperatures there was more thermal energy available for dislocation activation and mobilization. The influence of temperature on the local weld zones were evaluated by extending a specimen, containing just the parent material. A simulation of a virtual strain gauge across the monolithic specimen’s gauge length, revealed that necking occurred at the centre of the specimen which corresponded to the hot zone. In contrast, a simulation of virtual strain gauges across both welds revealed that necking occurred in the region between the HAZ and weld material. This finding inferred that the presence of a weld reduced the strength of the component, as the weld material was the weakest material. Furthermore, the in-service operating conditions was found to have significantly influenced the material behaviour of the welds. A weld that was exposed to a more elevated temperatures and loads, was found to have undergone a higher degree of material degradation, and strained to a larger extent when compared to a weld that was exposed to a more moderate operating environment.