Micro-fine sphericalpowders are recommended for selective laser melting(SLM). However, they are mostly expensive due to the complex manufacturing technique and low yield. In this paper, using lowcost treated hydride-d...Micro-fine sphericalpowders are recommended for selective laser melting(SLM). However, they are mostly expensive due to the complex manufacturing technique and low yield. In this paper, using lowcost treated hydride-dehydride(HDH) Ti powders, commercial pure Ti(CP-Ti) was successfully fabricated by SLM. After 4-h milling, the resulting powders become near-spherical with no obvious angularity, and have optimal flowability with the apparent density of 1.64 ± 0.02 g/cm^3, tap density of 2.10 ± 0.04 g/cm^3,angle of repose 40.11?±0.09?, and Carr's index of 77.74 ± 0.15. The microstructure was determined with full acicular martensitic β phase. The CP-Ti can achieve superior mechanical properties with the ultimate tensile strength of 876.1 ± 20.5 MPa and elongation of(14.7 ± 0.5)%, which exhibit distinctly competitive compared to the as-cast CP-Ti or Ti-6 Al-4 V. Excellent mechanical properties together with its low-cost make SLM-fabricated CP-Ti from modified HDH Ti powders show promising applications.展开更多
The presence ofα/αon priorβ/βgrain boundaries directly impacts the final mechanical properties of the titanium alloys.Theβ/βgrain boundary variant selection of titanium alloys has been assumed to be unlikely owi...The presence ofα/αon priorβ/βgrain boundaries directly impacts the final mechanical properties of the titanium alloys.Theβ/βgrain boundary variant selection of titanium alloys has been assumed to be unlikely owing to the high cooling rates in laser powder bed fusion(L-PBF).However,we hypothesize that powder characteristics such as morphology(non-spherical)and particle size(50–120μm)could affect the initial variant selection in L-PBF processed Ti-6Al-4V alloy by locally altering the cooling rates.Despite the high cooling rate found in L-PBF,results showed the presence ofβ/βgrain boundaryαlath growth inside two adjacent priorβgrains.Electron backscatter diffraction micrographs confirmed the presence ofβ/βgrain boundary variant selection,and synchrotron X-ray high-speed imaging observation revealed the role of the“shadowing effect”on the locally decreased cooling rate because of keyhole depth reduction and the consequentβ/βgrain boundaryαlath growth.The self-accommodation mechanism was the main variant selection driving force,and the most abundantα/αboundary variant was type 4(63.26°//[10553¯]).The dominance of Category IIαlath clusters associated with the type 4α/αboundary variant was validated using the phenomenological theory of martensite transformations and analytical calculations,from which the stress needed for theβ→αtransformation was calculated.展开更多
基金supported by Fundamental Reseearch Funds for the Central Universities (No. FRF-GF-17-B39)
文摘Micro-fine sphericalpowders are recommended for selective laser melting(SLM). However, they are mostly expensive due to the complex manufacturing technique and low yield. In this paper, using lowcost treated hydride-dehydride(HDH) Ti powders, commercial pure Ti(CP-Ti) was successfully fabricated by SLM. After 4-h milling, the resulting powders become near-spherical with no obvious angularity, and have optimal flowability with the apparent density of 1.64 ± 0.02 g/cm^3, tap density of 2.10 ± 0.04 g/cm^3,angle of repose 40.11?±0.09?, and Carr's index of 77.74 ± 0.15. The microstructure was determined with full acicular martensitic β phase. The CP-Ti can achieve superior mechanical properties with the ultimate tensile strength of 876.1 ± 20.5 MPa and elongation of(14.7 ± 0.5)%, which exhibit distinctly competitive compared to the as-cast CP-Ti or Ti-6 Al-4 V. Excellent mechanical properties together with its low-cost make SLM-fabricated CP-Ti from modified HDH Ti powders show promising applications.
基金supported in part by the Pennsylvania Infrastructure Technology Alliance,a partnership of Carnegie Mellon,Lehigh University,and the Commonwealth of Pennsylvania’s Department of Community and Economic Development(DCED)The authors recognize Reading Alloys(formerly affiliated with AMETEK Inc.,now a part of Kymera International),especially Muktesh Paliwal and Mike Marucci,for providing the Ti-6Al-4V powder used in this work and for assistance with the study+1 种基金This work was performed under the auspices of the U.S.Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344 and IM release number#LLNL-JRNL-838778The authors acknowledge partial support from the National Science Foundation under grant number DMR-2050916.IG appreciates the financial support from the Gallogly College of Engineering at the University of Oklahoma.
文摘The presence ofα/αon priorβ/βgrain boundaries directly impacts the final mechanical properties of the titanium alloys.Theβ/βgrain boundary variant selection of titanium alloys has been assumed to be unlikely owing to the high cooling rates in laser powder bed fusion(L-PBF).However,we hypothesize that powder characteristics such as morphology(non-spherical)and particle size(50–120μm)could affect the initial variant selection in L-PBF processed Ti-6Al-4V alloy by locally altering the cooling rates.Despite the high cooling rate found in L-PBF,results showed the presence ofβ/βgrain boundaryαlath growth inside two adjacent priorβgrains.Electron backscatter diffraction micrographs confirmed the presence ofβ/βgrain boundary variant selection,and synchrotron X-ray high-speed imaging observation revealed the role of the“shadowing effect”on the locally decreased cooling rate because of keyhole depth reduction and the consequentβ/βgrain boundaryαlath growth.The self-accommodation mechanism was the main variant selection driving force,and the most abundantα/αboundary variant was type 4(63.26°//[10553¯]).The dominance of Category IIαlath clusters associated with the type 4α/αboundary variant was validated using the phenomenological theory of martensite transformations and analytical calculations,from which the stress needed for theβ→αtransformation was calculated.
