The Mg-Gd-Y-Zn-Zr alloys are representational and potential age-hardening systems as reported in the past ten years,but their mechanical properties are still dependent on the grain size and its distribution.The effect...The Mg-Gd-Y-Zn-Zr alloys are representational and potential age-hardening systems as reported in the past ten years,but their mechanical properties are still dependent on the grain size and its distribution.The effect of bimodal structure on mechanical properties of Mg-8Gd-3Y-0.5Zr alloy with bimodal grain size distributions was investigated.The results suggested that the volume fraction of fine grain(FG)and coarse grain(CG)could be controlled by combined processes of hot forging,extrusion and annealing.And for the present alloys with bimodal grain size distribution,the improvement of strength is still attributed to the grain refinement.The morphology of bimodal grain size distribution has a marked impact on the ductility of the alloy,i.e.with the increase of coarse grain volume fraction,the elongation to failure increases at the beginning and then decreases.The mechanism of the toughening effect of bimodal grain size distribution on the Mg-Gd-Y-Zn-Zr alloys with bimodal grain size structure has been discussed.展开更多
In order to improve the wear resistance of coarse-grained WC-Co cemented carbides,the fine WC powder were used to reinforce the metallic binder.These WC-Co-based cemented carbides having bimodal WC grain size distribu...In order to improve the wear resistance of coarse-grained WC-Co cemented carbides,the fine WC powder were used to reinforce the metallic binder.These WC-Co-based cemented carbides having bimodal WC grain size distributions were synthesized by liquid phase sintering.For comparison,the cemented carbides having unimodal WC grain size distributions were synthesized.The microstructure,hardness,fracture toughness and wear resistance of these cemented carbides were investigated.The results show that adding fine WC powder is an effective method to improve the wear resistance of coarsegrained WC-Co cemented carbides.The WC size,mean free path and fracture toughness decrease with the addition of fine WC powder,while the hardness exhibits an opposite trend.The impact-wear coefficient of bimodal distribution cemented carbides is noticeably lower than that of the unimodal one with the same hardness,which means that the cemented carbides with bimodal grain structure have better combination of hardness and impact-abrasive wear resistance.The impact-abrasive wear mechanism of the bimodal cemented carbides is that the fine WC grains prevent abrasive wear and the coarse WC grains prevent impact wear.展开更多
为了探究孔隙含水层的非均质性对注水井附近溶质运移的控制机理以及溶质羽的空间分布特征,基于美国MADE场地含水层地质统计学数据,利用T-PROGS(transition probability geostatistical software)构建了三维径向非均质随机模型;并结合MOD...为了探究孔隙含水层的非均质性对注水井附近溶质运移的控制机理以及溶质羽的空间分布特征,基于美国MADE场地含水层地质统计学数据,利用T-PROGS(transition probability geostatistical software)构建了三维径向非均质随机模型;并结合MODFLOW和MT3DMS模块模拟了注水井附近的溶质运移过程,研究了沉积相不同空间结构对溶质运移过程的影响。结果表明:在非均质含水层注水井附近普遍存在双峰反常运移现象;径向溶质运移受高渗透性沉积相的沉积长度和厚度影响较大,沉积长度越大溶质质量空间分布曲线双峰现象越明显,尤其当沉积长度扩大到1.75倍时,双峰现象最明显;通过模拟结果可以得出高渗透性沉积相所在位置与高流速优先流所处位置呈一定的正相关性。总体而言,高渗透性的含水介质在冲洪积孔隙含水层中具有很强的连通性,易形成优先水流通道,导致溶质沿快速和慢速两种通道运移,从而使得穿透曲线出现双峰现象。展开更多
Previous studies have shown that the fatigue life distribution of metal materials fabricated with Additive Manufacturing(AM) methods, such as Direct Energy Deposited(DED) Ti-6.5Al-2Zr-1Mo-1V alloys, exhibits two peaks...Previous studies have shown that the fatigue life distribution of metal materials fabricated with Additive Manufacturing(AM) methods, such as Direct Energy Deposited(DED) Ti-6.5Al-2Zr-1Mo-1V alloys, exhibits two peaks. To promote the application of AM in aerospace and other engineering fields, developing a fatigue strength evaluation method suitable for AM materials based on their unique fatigue behaviours and fatigue life distributions is necessary. In this paper, a novel Detail Fatigue Rating(DFR) method was developed to evaluate the fatigue strength of DED Ti-6.5Al-2Zr-1Mo-1V based on a bimodal Weibull distribution and the excessive restriction on the allowable stress of potential was improved. Meanwhile, a Bimodal Weibull distribution model for fatigue life and its parameter estimation method were established based on a twoparameter Weibull distribution. The fatigue life at a specific reliability level and confidence level was calculated by using the bootstrap method. The calculation results showed that fatigue life estimated by using the bimodal Weibull distribution at the high reliability level and high confidence level is higher than that estimated by using the two-parameter Weibull distribution. Furthermore,The S-N curve at the specified confidence level and reliability level was fitted.展开更多
基金supports of the National Key Research and Development Plan(Grant Nos.2016YFB0701201 and 2016YFB0301103)the National Natural Science Foundation of China(Grant Nos.51771109 and 51631006).
文摘The Mg-Gd-Y-Zn-Zr alloys are representational and potential age-hardening systems as reported in the past ten years,but their mechanical properties are still dependent on the grain size and its distribution.The effect of bimodal structure on mechanical properties of Mg-8Gd-3Y-0.5Zr alloy with bimodal grain size distributions was investigated.The results suggested that the volume fraction of fine grain(FG)and coarse grain(CG)could be controlled by combined processes of hot forging,extrusion and annealing.And for the present alloys with bimodal grain size distribution,the improvement of strength is still attributed to the grain refinement.The morphology of bimodal grain size distribution has a marked impact on the ductility of the alloy,i.e.with the increase of coarse grain volume fraction,the elongation to failure increases at the beginning and then decreases.The mechanism of the toughening effect of bimodal grain size distribution on the Mg-Gd-Y-Zn-Zr alloys with bimodal grain size structure has been discussed.
基金financially supported by the National Natural Science Foundation of China(No.51101021)。
文摘In order to improve the wear resistance of coarse-grained WC-Co cemented carbides,the fine WC powder were used to reinforce the metallic binder.These WC-Co-based cemented carbides having bimodal WC grain size distributions were synthesized by liquid phase sintering.For comparison,the cemented carbides having unimodal WC grain size distributions were synthesized.The microstructure,hardness,fracture toughness and wear resistance of these cemented carbides were investigated.The results show that adding fine WC powder is an effective method to improve the wear resistance of coarsegrained WC-Co cemented carbides.The WC size,mean free path and fracture toughness decrease with the addition of fine WC powder,while the hardness exhibits an opposite trend.The impact-wear coefficient of bimodal distribution cemented carbides is noticeably lower than that of the unimodal one with the same hardness,which means that the cemented carbides with bimodal grain structure have better combination of hardness and impact-abrasive wear resistance.The impact-abrasive wear mechanism of the bimodal cemented carbides is that the fine WC grains prevent abrasive wear and the coarse WC grains prevent impact wear.
文摘为了探究孔隙含水层的非均质性对注水井附近溶质运移的控制机理以及溶质羽的空间分布特征,基于美国MADE场地含水层地质统计学数据,利用T-PROGS(transition probability geostatistical software)构建了三维径向非均质随机模型;并结合MODFLOW和MT3DMS模块模拟了注水井附近的溶质运移过程,研究了沉积相不同空间结构对溶质运移过程的影响。结果表明:在非均质含水层注水井附近普遍存在双峰反常运移现象;径向溶质运移受高渗透性沉积相的沉积长度和厚度影响较大,沉积长度越大溶质质量空间分布曲线双峰现象越明显,尤其当沉积长度扩大到1.75倍时,双峰现象最明显;通过模拟结果可以得出高渗透性沉积相所在位置与高流速优先流所处位置呈一定的正相关性。总体而言,高渗透性的含水介质在冲洪积孔隙含水层中具有很强的连通性,易形成优先水流通道,导致溶质沿快速和慢速两种通道运移,从而使得穿透曲线出现双峰现象。
基金the support from the National Key Research and Development Program of China(No.2017YFB1104003)National Natural Science Foundation of China(No.11772027)Aeronautical Science Foundation of China(No.201909051002)。
文摘Previous studies have shown that the fatigue life distribution of metal materials fabricated with Additive Manufacturing(AM) methods, such as Direct Energy Deposited(DED) Ti-6.5Al-2Zr-1Mo-1V alloys, exhibits two peaks. To promote the application of AM in aerospace and other engineering fields, developing a fatigue strength evaluation method suitable for AM materials based on their unique fatigue behaviours and fatigue life distributions is necessary. In this paper, a novel Detail Fatigue Rating(DFR) method was developed to evaluate the fatigue strength of DED Ti-6.5Al-2Zr-1Mo-1V based on a bimodal Weibull distribution and the excessive restriction on the allowable stress of potential was improved. Meanwhile, a Bimodal Weibull distribution model for fatigue life and its parameter estimation method were established based on a twoparameter Weibull distribution. The fatigue life at a specific reliability level and confidence level was calculated by using the bootstrap method. The calculation results showed that fatigue life estimated by using the bimodal Weibull distribution at the high reliability level and high confidence level is higher than that estimated by using the two-parameter Weibull distribution. Furthermore,The S-N curve at the specified confidence level and reliability level was fitted.
