通过微波等离子体化学气相沉积(Microwave plasma chemical vapor deposition,MPCVD)方法制备了不同工艺条件下的多晶金刚石散热片,并对其热导率、翘曲、表面形貌、晶体取向和拉曼光谱进行测试和分析。结果表明,甲烷浓度和生长温度对金...通过微波等离子体化学气相沉积(Microwave plasma chemical vapor deposition,MPCVD)方法制备了不同工艺条件下的多晶金刚石散热片,并对其热导率、翘曲、表面形貌、晶体取向和拉曼光谱进行测试和分析。结果表明,甲烷浓度和生长温度对金刚石生长速率和品质都有较大影响,适当降低甲烷浓度并提高生长温度有助于制备低翘曲、高热导率的高品质多晶金刚石散热片。展开更多
通过改变激光粉末床熔融(laser powder bed fusion,LPBF)的扫描速度研究IN738LC合金组织演化及各向异性机制,采用光学显微镜(optical microscopy,OM)及扫描电镜(scanning electron microscopy,SEM)对组织形貌特征进行表征分析,通过X射...通过改变激光粉末床熔融(laser powder bed fusion,LPBF)的扫描速度研究IN738LC合金组织演化及各向异性机制,采用光学显微镜(optical microscopy,OM)及扫描电镜(scanning electron microscopy,SEM)对组织形貌特征进行表征分析,通过X射线衍射(X-ray diffraction,XRD)对其织构性进行测试,使用显微硬度仪对显微硬度及各向异性进行评价.结果表明,随着扫描速度从800 mm/s提高到1600 mm/s,晶粒尺寸得到显著细化,且晶粒长轴取向由低扫描速度下沿建造方向择优,转变为高扫描速度下的沿熔池边界法线方向择优.这是因为低扫描速度下高熔池重熔率导致更多枝晶沿建造方向外延择优生长.这种沿建造方向的强择优生长同时导致(200)面沿建造方向择优的织构性,且这种织构强度随扫描速度增加而降低.这种(200)面沿建造方向择优织构还导致水平截面软轴居多,进而导致水平显微硬度低于侧界面显微硬度的各向异性.展开更多
The inherent brittle behavior and ductile-to-brittle transition(DBT)mechanism of Sn−3.0Ag−0.5Cu(SAC305)solder alloy at the liquid nitrogen temperature(LNT,77 K)were investigated through uniaxial tensile experiments co...The inherent brittle behavior and ductile-to-brittle transition(DBT)mechanism of Sn−3.0Ag−0.5Cu(SAC305)solder alloy at the liquid nitrogen temperature(LNT,77 K)were investigated through uniaxial tensile experiments conducted at different temperatures.Dynamic recovery and recrystallization of SAC305 solder alloy at room temperature(RT,293 K)activate a softening process.Conversely,intersecting and none-intersecting deformation twins,embedded in body-centered tetragonal Sn,enhance tensile strength and stabilize strain hardening rate,while suppressing the elongation of the alloy at LNT.The irreconcilable velocity difference between twin thickening(~8μm/s)and dislocation slip(4μm/s)results in premature brittle fracture,during the linear hardening and DBT.Moreover,the secondary phases degrade the mechanical property of SAC305 solder alloy,and micro-cracks appear between Cu_(6)Sn_(5)and Ag_(3)Sn in the eutectic matrix.展开更多
文摘通过微波等离子体化学气相沉积(Microwave plasma chemical vapor deposition,MPCVD)方法制备了不同工艺条件下的多晶金刚石散热片,并对其热导率、翘曲、表面形貌、晶体取向和拉曼光谱进行测试和分析。结果表明,甲烷浓度和生长温度对金刚石生长速率和品质都有较大影响,适当降低甲烷浓度并提高生长温度有助于制备低翘曲、高热导率的高品质多晶金刚石散热片。
文摘通过改变激光粉末床熔融(laser powder bed fusion,LPBF)的扫描速度研究IN738LC合金组织演化及各向异性机制,采用光学显微镜(optical microscopy,OM)及扫描电镜(scanning electron microscopy,SEM)对组织形貌特征进行表征分析,通过X射线衍射(X-ray diffraction,XRD)对其织构性进行测试,使用显微硬度仪对显微硬度及各向异性进行评价.结果表明,随着扫描速度从800 mm/s提高到1600 mm/s,晶粒尺寸得到显著细化,且晶粒长轴取向由低扫描速度下沿建造方向择优,转变为高扫描速度下的沿熔池边界法线方向择优.这是因为低扫描速度下高熔池重熔率导致更多枝晶沿建造方向外延择优生长.这种沿建造方向的强择优生长同时导致(200)面沿建造方向择优的织构性,且这种织构强度随扫描速度增加而降低.这种(200)面沿建造方向择优织构还导致水平截面软轴居多,进而导致水平显微硬度低于侧界面显微硬度的各向异性.
基金supported by the National Natural Science Foundation of China(No.51775141)。
文摘The inherent brittle behavior and ductile-to-brittle transition(DBT)mechanism of Sn−3.0Ag−0.5Cu(SAC305)solder alloy at the liquid nitrogen temperature(LNT,77 K)were investigated through uniaxial tensile experiments conducted at different temperatures.Dynamic recovery and recrystallization of SAC305 solder alloy at room temperature(RT,293 K)activate a softening process.Conversely,intersecting and none-intersecting deformation twins,embedded in body-centered tetragonal Sn,enhance tensile strength and stabilize strain hardening rate,while suppressing the elongation of the alloy at LNT.The irreconcilable velocity difference between twin thickening(~8μm/s)and dislocation slip(4μm/s)results in premature brittle fracture,during the linear hardening and DBT.Moreover,the secondary phases degrade the mechanical property of SAC305 solder alloy,and micro-cracks appear between Cu_(6)Sn_(5)and Ag_(3)Sn in the eutectic matrix.
