Enhanced mechanical properties and formability of 316L stainless steel materials 3D-printed using selective laser melting

This study is conducted to develop an innovative and attractive selective laser melting(SLM)method to produce 316 L stainless steel materials with excellent mechanical performance and complex part shape.In this work,the subregional manufacturing strategy,which separates the special parts from the components using an optimized process,was proposed.The results showed that produced 316 L materials exhibited superior strength of^755 MPa and good ductility.In the as-built parts,austenite with preferred orientation of the(220)plane,δ-ferrite,and a small amount of CrO phases were present.In addition,the crystal size was fine,which contributed to the enhancement of the parts’mechanical properties.The structural anisotropy mechanism of the materials was also investigated for a group of half-sized samples with variable inclination directions.This technique was used to fabricate a set of impellers with helical bevels and high-precision planetary gears,demonstrating its strong potential for use in practical applications.

Sliding wear behaviour of Fe/316L/430-Ti(C,N)composites prepared via spark plasma sintering and subsequent heat treatment

A series of novel steel-Ti(C,N)composites was fabricated by spark plasma sintering(SPS)and subsequent heat treatment.The hardness,indentation fracture resistance,and wear behaviour of the steel-Ti(C,N)composites were compared with those of the unreinforced samples,and their potentials were assessed by comparison with traditional cermet/hardmetal systems.The results showed that with the addi-tion of 20wt%Ti(C,N),the wear rates of the newly examined composites reduced by a factor of about 2 to 4 and were comparable to those of cermets and hardmetals.The martensitic transformation of the steel matrix and the formation of in situ carbides induced by heat treatment en-hanced the wear resistance.Although the presence of excessive in situ carbides improved the hardness,the low indentation fracture resistance(IFR)value resulted in brittle fracture,which in turn resulted in poor wear property.Moreover,the operative wear mechanisms were investig-ated.This study provides a practical and cost-effective approach to prepare steel-Ti(C,N)composites as potential wear-resistant materials.

Microstructure and mechanical properties of WC-(Ti,M)(C,N)-Co cemented carbides with different nitrogen contents

Three kinds of(Ti,M)(C_(1-x),N_(x))(M=Ta,Nb,W) quaternary solid-solution powders with various nitrogen contents were synthesized by carbothermal reductionnitridation(CRN) process.Effect of nitrogen content on the microstructure and mechanical properties of WC-(Ti,M)(C_(1-x),N_(x))-Co cemented carbides fabricated by sinterhot isostatic pressing(HIP) were systematically investigated in this paper.The results show that the nitrogen content in the carbonitride raw powders strongly influences the morphology,the grain size and the compositions of the cemented carbides.All the cemented carbides with different nitrogen contents have a similar microstructural appearance:weak core-rim structure consisting of solidsolution phase embedded in WC-Co system.It is also observed that the carbonitride solid solution could somewhat reduce the WC grain growth,and the effectiveness of refining and the rim thickness are sensitively related to the nitrogen content of(Ti,M)(C_(1-x),N_(x)) solid solutions.In addition,with an increase in the nitrogen content,mechanical properties of these hard metals are enhanced,which were discussed in terms of the constituent,the microstructure and the solution behavior of the carbonitride solid solutions.

Microwave sintering of TiCN-based cermets prepared from electroless Co-coated(Ti,W,Mo,V)CN powders

In this study,the densification and microstructure evolution of microwave sintered(Ti,W,Mo,V)CN-30 wt%Co cermets,which was prepared from electroless cobalt-coated submicron(Ti,W,Mo,V)CN powders,were investigated.The microwave sintering of mechanical milled powders as well as the conventional sintering of mechanical milled powders and Co-coated(Ti,M)CN powders was conducted as a comparison.Experimental results indicate that a slight densification is observed at sintering temperature of≤1100℃followed by a sharp shrinkage at the temperature range of 1200-1350℃due to the substantial formation of liquid phase at 1200℃.The 98.5%densification is obtained at 1375℃.Moreover,the samples sintered at 1375℃for 10 min have the micro structure with fine and homogeneous grains of about 700 nm.Compared to mechanical milling,electroless cobalt plating suppresses coalescence of neighboring grain at the solid-state sintering stage,thereby inhibiting grain growth.The mechanical properties of samples sintered at different temperatures for varied holding time were also discussed.

Microstructure and mechanical properties improvements in cemented carbides by(Cr,Mo,Ta)_(2)(C,N) inhibitors

Grain growth inhibitors can effectively suppress the grain size of tungsten carbide(WC),and consequently improve the hardness and strength of the cemented carbides;however,the toughness,one of the most important properties,usually deteriorates with inhibitors.Here,(Cr,Mo,Ta)_(2)(C,N) synthesized by carbothermal reductionnitridation was used as a novel inhibitor,and its effects on the microstructure and mechanical properties of the cemented carbides were investigated.The results showed that the cemented carbides containing(Cr,Mo,Ta)_(2)(C,N)outperformed its counterpart comprising the traditional inhibitors in comprehensive mechanical properties,which was mainly attributed to the better inhibition performance provided by the(Cr,Mo,Ta)_(2)(C,N) solid-solution powders.With the content of(Cr,Mo,Ta)_(2)(C,N) increasing from 0 wt% to 1.25 wt%,the average grain size of WC in the cemented carbides decreased from 0.85 to 0.60 μm firstly,and then increased to 0.64 μm.With 1.00 wt%(Cr,Mo,-Ta)_(2)(C,N) addition,the cemented carbides with the best performance of hardness(HV_(30)) of 15.55 GPa,transverse rupture strength of 4272 MPa,fracture toughness of13.91 MPa·m1/2 were obtained.The electron backscattered diffraction(EBSD) measurements showed that cemented carbides with(Cr,Mo,Ta)_(2)(C,N) processed more amount of∑2 boundary compared with the other specimens,which contributed to better fracture resistance.

Grain Refining Efficiency of SHS Al-Ti-B-C Master Alloy for Pure Aluminum and Its Effect on Mechanical Properties

A new Al-5Ti-0.75B-0.2C master alloy was successfully prepared by self-propagating high-temperature（SHS）reaction from an Al-Ti-B_4C system with molten Al.Microstructure and phase characterization of the prepared Al-5Ti-0.75B-0.2C master alloy show that the nearly spherical TiC particles,hexagonal or rectangular TiB_2 particles,and blocklike TiAl_3 particles distribute uniformly in the aluminum matrix.Grain refining test on commercial pure aluminum indicates that Al-5Ti-0.75B-0.2C master alloy exhibits a better grain refining performance than Al-5Ti-lB master alloy.By addition of 0.2 wt%Al-5Ti-0.75B-0.2C master alloy,the average grain size of a-Al can be effectively refined to160 ± 5 μm from about 3000 μm,and the tensile strength and elongation are increased by about 20%and 14.1%due to the grain refinement.