哈尔滨工业大学：《金属学与热处理》课程教学资源（PPT课件）第三章 二元合金相图和合金的凝固（3.2）匀晶相图及固溶体的结晶

§3.2幻晶相图及固落体的结晶」「 常见匀晶合金 Cu-Ni, Ag-Au NiO-MgO, Alo Cr-Mo, Cd-Mg, Fe-Ni Mo-W 在液态和固态下两组元均能完全无限互溶

§3.2 匀晶相图及固溶体的结晶 常见匀晶合金 Cu-Ni, Ag-Au, Cr-Mo, Cd-Mg, Fe-Ni, Mo-W NiO-MgO, Al2O3 - Cr2O3 在液态和固态下两组元均能完全无限互溶

§3.2幻晶相图及固落体的结晶」「 相图分析 t1温度一一开始结晶,尚无晶相 t2温度一一通过扩散达到平衡 平衡结晶过程 t3温度一一结晶结束 冷却曲线 结晶过程 相平衡组织形式 1500 t1 L1==a1 t 2 t4 L4==a4 1100 1000 时间 Ni20406080Cu Cu. 40%Cu-Ni平衡结晶成分变化和相平衡

§3.2 匀晶相图及固溶体的结晶 平衡结晶过程 相图分析 t1 温度－－开始结晶，尚无晶相 t2 温度－－通过扩散达到平衡 t3 温度－－结晶结束

结晶过程:形核和长大 形核方式:均匀形核和非均匀形核 形核条件:结构起伏能量起伏十成分起伏 差异:1异分结晶一一结晶时结晶出的固相与液相成分 不同,也称为选择性结晶 2变温结晶一一固溶体合金的结晶需要在一定温 度范围内进行。 平衡分配系数一一在一定温度下,固液两平衡相溶质浓 度之比值,用k表示

结晶过程：形核和长大 形核方式：均匀形核和非均匀形核 形核条件：结构起伏能量起伏＋成分起伏 差异：1 异分结晶－－结晶时结晶出的固相与液相成分 不同，也称为选择性结晶。 2变温结晶－－固溶体合金的结晶需要在一定温 度范围内进行。 平衡分配系数－－在一定温度下，固液两平衡相溶质浓 度之比值，用k0表示

固溶体长大机制的主要特征: 相界平衡造成相内浓度梯度 koCo Co 和 oC\-ti 起 koC C2 和Gta 达 到 相内扩散 造成 相界移动利起相界不平衡 B, B 固溶体长大与相平衡 易于形成树枝状

易于形成树枝状

§3.2幻晶相图及固落体的结晶」「 单相固溶体凝固 特点:扩散控制 平衡分配系数 液相 液相 定义:k。= 固相 k 国相线 固相 该值的含义: 合金偏析程度的大小。 5/ k Co 成分 (b)

§3.2 匀晶相图及固溶体的结晶

L 400 L (NL. MgIO 2000 NiO20406 s0 Meo Mole percent Mgo Design of a Refractory Brick Design a NiO-MgO refractory material that can be melted and cast at 2600'C but will not melt when placed into service at 2300C

Design of a Composite material One method to improve the fracture toughness of a ceramic material is to reinforce the ceramic matrix with ceramic fibers, a materials designer has suggested that Al,2O3 could be reinforced with 25%/ cr,o fibers which would interfere with the propagation of any cracks in the aluminia. The resulting composite is expected to operate under load at 2000.C for several months, Criticize the appropriateness of this design

One method to improve the fracture toughness of a ceramic material is to reinforce the ceramic matrix with ceramic fibers. A materials designer has suggested that Al2O3 could be reinforced with 25% Cr2O3 fibers, which would interfere with the propagation of any cracks in the aluminia. The resulting composite is expected to operate under load at 2000℃ for several months. Criticize the appropriateness of this design. Design of a Composite Material

1.500 1.400 L 1300 a+I 1.200 1.100 1.0 80.000 Tensile strengt 60.000 60 5=45 540.000 fe Elongation 20.000 Yield strength 0 C 80 Weight percent nickel

Design of a Melting Procedure for a Casting You need to produce a Cu-Ni alloy having a minimum yield strength of 20000psi, a minimum tensile strength of 60000psi and a minimum elongation of 20%o You have in your inventory a Cu-20%Ni alloy and lots of pure nickel. Design a method for producing 10kg castings having the required properties

You need to produce a Cu-Ni alloy having a minimum yield strength of 20000psi, a minimum tensile strength of 60000psi, and a minimum elongation of 20%. You have in your inventory a Cu-20%Ni alloy and lots of pure nickel. Design a method for producing 10kg castings having the required properties. Design of a Melting Procedure for a Casting

Cu-90oNi or cu-%o to 60%o Ni (10ko/35%Ni 100% 3.5 kg Ni required 20% 100% (x kg Cu-20% Ni) 100%)+(10xkgM10%3.kgNp 02x+10-x=3.5 6.5=08x x=8. 125 kg Cu-20% Ni 加热到1250°C

Cu-90%Ni or Cu-33% to 60% Ni 加热到1250℃