Microstructure and thermal stability of sintered pure tungsten processed by multiple direction compression

Multiple direction compression(MDC)was conducted on sintered pure tungsten(99.9%,mass fraction)with different reductions at 1423 K.The microstructure,microhardness and thermal stability of the MDC-processed samples were studied by X-ray diffraction(XRD),electron backscattered diffraction(EBSD)and differential scanning calorimetry(DSC)compared with those of the initial sintered tungsten.The results show that the dislocation density increases significantly with the reduction of MDC,ranging from 3.08×1014 m-2 for the initial sintered tungsten to 8.08×1014 m-2 for the tungsten after MDC with the reduction of 50%.The average grain size decreases from 83.8 to 14.7μm and the microhardness value increases from HV0.2 417 to HV0.2 521.The recrystallization temperature for the tungsten samples processed by MDC is approximately constant at around 1600 K.The MDC of sintered tungsten results in a decrease of grain size concurrent with an increase of uniformly distributed nucleation sites,which leads to the improvement of the thermal stability.

Microstructure and properties of hydrogenated TB8 alloy

Thermohydrogen processing can enhance workability, decrease flow stress and deforming tempera- ture of titanium alloys. In this study, thermohydrogen processing was carried out for metastable β-type TB8 alloy. The microstructures of hydrogenated TB8 alloy were investigated based on scanning electron microscopy （SEM）, transmission electronic microscopy （TEM） as well as X-ray diffraction （XRD） analysis. The results reveal that 6 hydride phase forms in the hydrogenated TB8 alloy, but the amount of β phase increases with hydrogen content increasing. Single β phase appears when the hydrogen content reaches 0.7 wt%. The alloying elements redistrib- ute in the hydrogenated TB8 alloy, and hydrogen leads to the reduction of the alloying elements in β phase. The room-temperature compression tests were performed on a MTS809 machine. It is found that the room-temperature yield strength of hydrogenated TB8 alloy decreases. And minimum yield strength is obtained at a hydrogen content of 0.5 wt%. The ductility does not decrease within 0.7 wt% hydrogen content. These results provide theoretical basis for improving the formability and promoting the applica- tions of TB8 alloy.

Microstructural evolution and fracture mechanism of a new AlZn-Mg-Cu-Zr alloy processed by equal-channel angular pressing

Equal-channel angular pressing(ECAP) is considered to be one of the most effective processing procedures to produce ultrafine-grained(UFG) materials.A new AI-ZnMg-Cu-Zr alloy was subjected to ECAP experiment in Route B_(C)(i.e.,rotated 90° in the same sense between each pass).The effect of ECAP on the microstructural evolution and fracture mechanism of the alloy was analyzed by optical microscope(OM),X-ray diffraction(XRD),tensile test(at room temperature),and scanning electron microscope(SEM).The results show that the main strengthening phase of the alloy is MgZn_(2),whose content increases apparently after ECAP,the dislocation density increases by one order of magnitude,the hardness value of the 1 pass ECAPed sample increases by 53 %,the ultimate tensile strength(UTS)increases by 29 %,and the true strain increases by 15.4 %.But the further increase in the strength with the passes increasing would cost a slight drop in the true strain.The morphology of the tensile dimples is converted from elongated one to equiaxed one with a uniform distribution of size and depth after pressing.