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Recent Submissions

Access status: Open Access ,
X-ray diffraction profile analysis of martensitic Ti6Al4V (ELI) parts produced by laser powder bed fusion
(MATEC Web of Conferences, 2023) Muiruri, Amos; Maringa, Maina; du Preez, Willie
The quantification of the density of defects in materials through non-destructive methods is of great interest to scientists and engineers. Xray diffraction (XRD) peak profile analysis is a valuable method that is often used to reveal important microstructural information, such as defects present in crystalline materials as well as crystallite size. In this study, the broadening of XRD peaks of martensitic Ti6Al4V (ELI) produced by laser powder bed fusion (LPBF) was studied following modified Williamson-Hall (MWH) and Warren-Averbach (WA) analytical methods. The level of defects in martensitic LPBF Ti6Al4V (ELI) was found to drastically reduce by at least 73% after exposing the material to stress-relieving heat treatment.
Access status: Open Access ,
VARIATION OF IMPACT TOUGHNESS OF AS-BUILT DMLS TI6AL4V (ELI) SPECIMENS WITH TEMPERATURE
(South African Journal of Industrial Engineering November, 2018-10-09) Muiruri, Amos; Maringa, Maina; du Preez, W.B.; Masu, L.M.
The response of direct metal laser sintering (DMLS) produced Ti6Al4V (ELI) to impact was investigated using an instrumented Charpy impact test machine and V-notch specimens. Impact toughness testing was conducted over the temperature range of -130oC to 250oC. The effect of the orientation of the V-notch, with reference to the base plate, was investigated. The results indicated that the samples that were produced with the V-notch facing the base plate (LO) had better values of impact toughness than those that were produced with the V-notch facing away from the base plate (UP) over most of the test temperatures. The study further established that as-built DMLS Ti6Al4V (ELI) retains appreciable notch toughness, even at extremely low temperatures.
Access status: Open Access ,
Validation of a Microstructure-Based Model for Predicting the High Strain Rate Flow Properties of Various Forms of Additively Manufactured Ti6Al4V(ELI) Alloy
(Metals, 2021-10-13) Muiruri, Amos; Maringa, Maina; du Preez, Willie
To increase the acceptance of direct metal laser sintered Ti6Al4V(Extra Low Interstitial—ELI)in industry, analytical models that can quantitatively describe the interrelationships between themicrostructural features, field variables, such as temperature and strain rate, and the mechanical properties are necessary. In the present study, a physical model that articulates the critical microstructuralfeatures of grain sizes and dislocation densities for use in predicting the mechanical properties ofadditively manufactured Ti6Al4V(ELI) was developed. The flow stress curves of different microstructures of the alloy were used to obtain and refine the parameters of the physical model. The averagegrain size of a microstructure was shown to influence the athermal part of yield stress, while theinitial dislocation density in a microstructure was seen to affect the shape of the flow stress curve.The viscous drag effect was also shown to play a critical role in explaining the upturn of flow stressat high strain rates. The microstructure-based constitutive model developed and validated in thisarticle using experimental data showed good capacity to predict the high strain rate flow propertiesof additively manufactured Ti6Al4V(ELI) alloy.
Access status: Open Access ,
The Effect of Temperature on the Microstructures of Additively Manufactured Ti6 Al4 V(Eli)
(Iranian Journal of Materials Science and Engineering, 2024-09) Moloi, Tumelo; Dzogbewu, Thywill Cephas; Maringa, Maina; Muiruri, Amos
The stability of microstructure at high temperatures is necessary for many applications. This paper presents investigations on the effect of changes in temperature on the microstructures of additively manufactured Ti6Al4V(ELI) alloy, as a prelude to high temperature fatigue testing of the material. In the present study, a Direct Metal Laser Sintering (DMLS) EOSINT M290 was used to additively manufacture test samples. Produced samples were stress relieved and half of these were then annealed at high temperatures. The samples were then heated from room temperature to various temperatures, held there for three hours and thereafter, cooled slowly in the air to room temperature. During tensile testing, the specimens was heated up to the intended test temperature and held there for 30 minutes, and then tensile loads applied to the specimens till fracture. Metallographic samples were then prepared for examination of their microstructures both at the fracture surfaces and away from them. The obtained results showed that changes in temperature do have effects on the microstructure and mechanical properties of Ti6Al4V(ELI) alloy. It is concluded in the paper that changes in temperature will affect the fatigue properties of the alloy.
Access status: Open Access ,
Statistical Analysis of the Distribution of the Schmid Factor in As-Built and Annealed Parts Produced by Laser Powder Bed Fusion
(Crystals, 2022-05-23) Muiruri, Amos; Maringa, Maina; du Preez, Willie
This study documents a systematic analysis of the global Schmid factor for differentdeformation mechanisms in α0/α and β-grains in different forms of direct metal laser sintered(DMLS) Ti6Al4V(ELI) based on EBSD data. A novelty of this study is the use of these data to calculatethe values of the Schmid factor and the subsequent determination of their distribution and frequency,which, when compared to the slip systems of crystal structures, helps in determining the favourableslip systems in play. Both retained β-grains and reconstructed prior β-grains were considered in thisanalysis. The reconstruction of the prior β-grains was executed using the Automatic Reconstructionof Parent Grain for EBSD data (ARPGE) program. The distribution of the global Schmid factorfor these Ti6Al4V phases was calculated using the MATLAB-based MTEX toolbox program. Thisanalysis of deformation modes in the α0/α-phase was based on a uniaxial load state acting on thex, y, and z axes, while only the load along the build direction (x-direction) was considered in theanalysis of deformation mechanisms in the β-phase of the alloy. The results of this study showedthat the DMLS build direction influenced the distribution of the global Schmid factor for the basalslip system of α0/α-grains in as-built specimens and those samples that were heat treated below theα→β transformation temperature.