选区激光熔化成形颗粒增强铝基复合材料综述

选区激光熔化(SLM)是一种新兴逐层增材制造技术,能够生成具有三维复杂结构的高性能构件。颗粒增强铝基复合材料(PAMCs)由于结合铝基体和增强相的优异特性在很多领域被认为是一种重要材料。基于SLM和PAMCs的综合优势,新型SLMPAMCs在近年来被陆续开发和研究。因而,本文总结当前有关SLMPAMCs的研究进展。首先,着重分析SLM PAMCs的凝固行为。其次,对高性能SLM PAMCs设计和制造中涉及的重要问题进行全面的讨论,其中包括增强相的选择、工艺参数对成形和微观结构的影响以及缺陷演变和相调控。第三,对SLM PAMCs的性能和增强机制进行系统讨论。最后,对高性能SLM PAMCs未来发展方向提出建设性的观点。

Achieving exceptional wear resistance in a crack-free high-carbon tool steel fabricated by laser powder bed fusion without pre-heating

Laser powder bed fusion(LPBF)for the fabrication of dense components used for tooling applications,is highly challenging.Residual stresses,which evolve in the additively manufactured part,are inherent to LPBF processing.An additional stress contribution in high-carbon steels arises from the austenite-to-martensite phase transformation,which may eventually lead to cracking or even delamination.As an alternative to pre-heating the base plate,which is not striven by industry,lowering the martensite content which forms in the part,is essential for the fabrication of dense parts by LPBF of high-carbon tool steels which are then adapted to LPBF.In this study,a successful strategy demonstrates the processing of the Fe85Cr4Mo1V1W8C1(wt%)high-carbon steel by LPBF into dense parts(99.8%).The hierarchical microstructure consists of austenitic and martensitic grains separated by elemental segregations in which nanoscopic carbide particles form a network.A high density of microsegregation was observed at the molten pool boundary ultimately forming a superstructure.The LPBF-fabricated steel shows a yield strength,ultimate compressive stress,and total strain of 1210 MPa,3556 MPa,and 27.4%,respectively.The mechanical and wear performance is rated against the industrially employed and highly wear-resistant 1.2379 tool steel taken as the reference.Despite its lower macro-hardness,the LPBF steel(58.6 HRC,0.0061 mm^(3) Nm^(-1))shows a higher wear resistance than the reference steel(62.6 HRC,0.0078 mm^(3) Nm^(-1)).This behavior results from the wear-induced formation of martensite in a microscale thick layer directly at the worn surface,as it was proven via high-energy X-ray diffraction mapping.

Selective Laser Melting of Al-7Si-0.5Mg-0.5Cu:Effect of Heat Treatment on Microstructure Evolution,Mechanical Properties and Wear Resistance

Al-7Si-0.5Mg-0.5Cu alloy specimens have been fabricated by selective laser melting(SLM).In this study,the effects of solution treatment,quenching,and artifi cial aging on the microstructural evolution,as well as mechanical and wear properties,have been investigated.The as-prepared samples show a heterogeneous cellular microstructure with two different cell sizes composed ofα-Al and Si phases.After solution-treated and quenched(SQ)heat treatment,the cellular microstructure disappears,and coarse and lumpy Si phase precipitates and a rectangular Cu-rich phase were observed.Subsequent aging after solution-treated and quenched(SQA)heat treatment causes the formation of nanosized Cu-rich precipitates.The asprepared SLMs sample has good mechanical properties and wear resistance(compressive yield strength:215±6 MPa and wear rate 2×10^(-13)m^(3)/m).The SQ samples with lumpy Si particles have the lowest strength of 167±13 MPa and the highest wear rate of 6.18×10^(1-13)m^(3)/m.The formation of nanosized Cu-rich precipitates in the SQA samples leads to the highest compressive yield strength of 233±6 MPa and a good wear rate of 5.06×10^(-13)m^(3)/m.

Effect of Powder Particle Shape on the Properties of In Situ Ti–TiB Composite Materials Produced by Selective Laser Melting

This work studied the preparation of starting powder mixture influenced by milling time and its effect on the particle morphology （especially the shape） and, consequently, density and compression properties of in situ Ti-TiB composite materials produced by selective laser melting （SLM） technology. Starting powder composite system was prepared by mixing 95 wt% commercially pure titanium （CP-Ti） and 5 wt% titanium diboride （TiB2） powders and subsequently milled for two different times （i.e. 2 h and 4 h）. The milled powder mixtures after 2 h and 4 h show nearly spherical and irregular shape, respectively. Subsequently, the resultant Ti-5 wt% TiB2 powder mixtures were used for SLM processing. Scanning electron microscopy image of the SLM-processed Ti-TiB composite samples show needle-shape TiB phase distributed across the Ti matrix, which is the product of an in-situ chemical reaction between Ti and TiB2 during SLM. The Ti-TiB composite samples prepared from 2 h and 4 h milled Ti-TiB2 powders show different relative densities of 99.5% and 95.1%, respectively. Also, the compression properties such as ultimate strength and compression strain for the 99.5% dense composite samples is 1421 MPa and 17.8%, respectively, which are superior to those （883 MPa and 5.5%, respectively） for the 95.1% dense sample. The results indicate that once Ti and TiB2 powders are connected firmly to each other and powder mixture of nearly spherical shape is obtained, there is no additional benefit in increasing the milling time and, instead, it has a negative effect on the density （i.e. increasing porosity level） of the Ti-TiB composite materials and their mechanical properties.

Mechanical behavior and deformation mechanism of shape memory bulk metallic glass composites synthesized by powder metallurgy

The synthesis of martensitic or shape-memory bulk metallic glass composites(BMGCs)via solidification of the glass-forming melts requires the meticulous selection of the chemical composition and the proper choice of the processing parameters in order to ensure that the glassy matrix coexists with the desired amount of austenitic phase.Unfortunately,a relatively limited number of such systems,where austenite and glassy matrix coexist over a wide range of compositions,is available.Here,we study the effective-ness of powder metallurgy as an alternative to solidification for the synthesis of shape memory BMGCs.Zr_(48)Cu_(36)Al_(8)Ag_(8)matrix composites with different volume fractions of Ni_(50.6)Ti_(49.4)are fabricated using hot pressing and their microstructure,mechanical properties and deformation mechanism are investigated employing experiments and simulations.The results demonstrate that shape-memory BMGCs with tun-able microstructures and properties can be synthesized by hot pressing.The phase stability of the glass and austenitic components across a wide range of compositions allows us to examine fundamental as-pects in the field of shape memory BMGCs,including the effect of the confining stress on the martensitic transformation exerted by the glassy matrix,the contribution of each phase to the plasticity and the mechanism responsible for shear band formation.The present method gives a virtually infinite choice among the possible combinations of glassy matrices and shape memory phases,expanding the range of accessible shape memory BMGCs to systems where the glassy and austenitic phases do not form simul-taneously using the solidification route.