Effects of cubic carbides and La additions on WC grain morphology,hardness and toughness of WC-Co alloys

Effects of Cr3C2,VC and La2O3 additions on the WC grain morphology,hardness and toughness of WC-10Co alloys were investigated.To intensify the grain growth driving force,nano W and nano C,instead of the conventionally used WC,were used as the starting materials.To obtain a three-dimensional WC grain morphology,the natural sinter skins of the alloys were observed directly by scanning electron microscopy.It is shown that the additions have a strong ability in regulating the WC grain morphological and grain size distribution characteristics and the combinations of hardness and toughness.Due to the formation of regular and homogeneous triangular platelet WC grains,WC-10Co-0.6Cr3C2-0.06La2O3 alloy shows an excellent combination of hardness and toughness.The morphological regulation mechanism,the relationship between the WC grain morphology and the properties were discussed.

EFFECTS OF MISCHMETAL ADDITION ON THE CAST MICROSTRUCTURE OF 6063 ALLOYS

Effect of mischmetal addition on the cast microstructure of 6063 alloys has been investigated by means of optical microscopy, TEM and anode filming etc. The results show that there is a critical content of fining dendrite structure by adding mischmetal to 6063 alloys. This critical mischmetal content is about 0.15%. Only when the mischmetal content is above 0.15%, the secondary dendrite arm spacing decreased and eutectic structure fined. The cast grain is obviously refined when the content of mischmetal is lower. Consideration from the cast structure, the suitable mischmetal content in 6063 alloys is 0.20%.

多根棒料半封闭式剪切模设计

通过对稀土合金粒制件的剪切工艺进行了分析,介绍了模具结构和工作过程,提出了模具主要工作部分零件的设计要点,满足了大批量生产的要求,对同类型制件的加工提供了借鉴。

Microstructure and mechanical properties of high strength Mg−15Gd−1Zn−0.4Zr alloy additive-manufactured by selective laser melting process

In order to verify the feasibility of producing Mg−rare earth(RE)alloy by selective laser melting(SLM)process,the microstructure and mechanical properties of Mg−15Gd−1Zn−0.4Zr(wt.%)(GZ151K)alloy were investigated.The results show that fine grains(~2μm),fine secondary phases and weak texture,were observed in the as-fabricated(SLMed)GZ151K Mg alloy.At room temperature,the SLMed GZ151K alloy has a yield strength(YS)of 345 MPa,ultimate tensile strength(UTS)of 368 MPa and elongation of 3.0%.After subsequent aging(200℃,64 h,T5 treatment),the YS,UTS and elongation of the SLMed-T5 alloy are 410 MPa,428 MPa and 3.4%,respectively,which are higher than those of the conventional cast-T6 alloy,especially with the YS increased by 122 MPa.The main strengthening mechanisms of the SLMed GZ151K alloy are fine grains,fine secondary phases and residual stress,while after T5 treatment,the YS of the alloy is further enhanced by precipitates.

Effect of Nd addition on microstructure and tensile properties of laser additive manufactured TC11 titanium alloy

Single-layer and multilayer laser additive manufacturing(LAM)for TC11 alloy with different Nd additions was conducted and the effect of Nd addition on microstructure and properties was studied.With the addition of Nd,the aspect ratio of melting pools of single-layer specimens increases and the columnar-to-equiaxed transition occurs.The originalβgrain size andαplate width of TC11−1.0Nd are significantly reduced compared with those of pure TC11 specimens.It is proposed that the evenly distributed fine Nd_(2)O_(3) precipitates of about 1.51μm are formed preferentially during rapid solidification of melting pool,and they serve as heterogeneous nucleation particles to refine the microstructure in the subsequent solidification and solid-state phase transformation.Due to the multiple effects of Nd on the microstructure,the ultimate tensile strength of TC11−1.0Nd increases,while the yield strength,ductility and microhardness decrease compared with those of pure TC11.