硼化物原位自生增强TiAl基复合材料的组织演化、热变形行为及加工工艺设计

硼元素添加造成的相转变和硼化物析出等因素会对原位TiAl基复合材料显微组织演化及热变形行为产生影响。利用等温压缩实验、扫描电子显微技术以及透射电子显微技术等研究材料的动态再结晶和动态回复机制,并计算出其表现变形激活能为691.506 k J/mol。在1100~1200℃温度区间,再结晶γ和α晶粒的形核长大分别主导α2→α相转变温度上、下的热变形行为。α相的动态回复主导材料在1250℃低应变速率下的热变形行为;同时,硼元素会提高α相含量,降低γ→α和α2→α相转变温度,进而促进加载过程中回复α相晶粒的形核长大。根据新建的本构模型,对TiAl基复合材料的变形机制和加工工艺进行详细阐述.

AlLi相对Mg−Li合金热压缩变形行为和动态再结晶的影响

采用等温热压缩实验研究含有AlLi相的Mg−5Li−3Al−2Zn(LAZ532)合金的热变形行为;变形温度和应变速率范围分别为473~623 K和0.001~1 s^(−1)。LAZ532合金热变形过程中AlLi相能够阻碍位错运动,从而显著提高合金的峰值应力值。为精确预测LAZ532合金的热变形行为,构建相应的应变补偿Arrhenius本构模型,预测结果与实验结果吻合良好。基于Murty准则,建立相应的热加工图,合理的加工区域在538~623 K和0.001~0.01 s^(−1)范围内。在高应变速率变形条件下,AlLi相不利于LAZ532合金在热压缩过程中的流动稳定性和动态再结晶。此外,变形温度会改变LAZ532合金的动态再结晶形核机制。

Prediction of grain scale plasticity of NiTi shape memory alloy based on crystal plasticity finite element method

Grain scale plasticity of NiTi shape memory alloy(SMA)during uniaxial compression deformation at 400℃was investigated through two-dimensional crystal plasticity finite element simulation and corresponding analysis based on the obtained orientation data.Stress and strain distributions of the deformed NiTi SMA samples confirm that there exhibits a heterogeneous plastic deformation at grain scale.Statistically stored dislocation(SSD)density and geometrically necessary dislocation(GND)density were further used in order to illuminate the microstructure evolution during uniaxial compression.SSD is responsible for sustaining plastic deformation and it increases along with the increase of plastic strain.GND plays an important role in accommodating compatible deformation between individual grains and thus it is correlated with the misorientation between neighboring grains,namely,a high GND density corresponds to large misorientation between grains and a low GND density corresponds to small misorientation between grains.

Correction to:Influence of Extrusion Speed on the Microstructure Evolution,Interface Bonding and Mechanical Response of Mg MB26/Al 7075 Composite Rod

Correction to:Acta Metallurgica Sinica(English Letters)(2019)32:253-262 https://doi.org/10.1007/s40195-018-0838-x Errorin Table In the original publication[1],there was an error in the contents of Mn element and Cr element in Table 1.The corrected Table 1 appears below.

Influence of Extrusion Speed on the Microstructure Evolution, Interface Bonding and Mechanical Response of Mg MB26/Al 7075 Composite Rod

The Mg MB26/Al 7075 composite rod,in which Mg MB26 serves as the sleeve and Al 7075 serves as the core,is fabricated via the process of co-extrusion.The influence of extrusion speed on the microstructure evolution,interface bonding and mechanical response of the Mg MB26/Al 7075 composite rod is investigated.The results show that the typical extrusion texture of Mg sleeve does not change during co-extrusion;however,the average grain size in the Mg sleeve slightly changes from 1.57 lm in the case of extrusion speed of 0.3 mm/s to 2.78 lm in the case of extrusion speed of2.1 mm/s.The thickness of interface transition layer increases significantly from 5.5 to 50 lm,and therefore,the interface bonding becomes deteriorative with increasing extrusion speed;in particular,many cavities emerge in the case of 1.2 and2.1 mm/s.