Concurrent nucleation, formation and growth of two intermetallic compounds (Cu6Sn5 and Cu3Sn) during the early stages of lead-free soldering

This study investigates the concurrent nucleation, formation and growth of two intermetallic compounds (IMCs), Cu₆Sn₅ (η) and Cu₃Sn (ε), during the early stages of soldering in the Cu-Sn system. The nucleation, formation and growth of the IMC layers is simulated through a multiphase-field model [1] and [2] in which the concurrent nucleation of both IMC phases is considered to be a stochastic Poisson process with nucleation rates calculated from classical nucleation theory [3]. CALPHAD thermodynamic models are used to calculate the local contributions to the free energy of the system and the driving forces for precipitation of the IMC phases. The nucleation parameters of the η phase are estimated from experimental results [4] and those of the ε phase are assumed to be similar. A parametric investigation of the effects of model parameters (e.g. grain boundary (GB) diffusion rates, interfacial and GB energies) on morphological evolution and IMC layer growth rate is presented and compared with previous works in which nucleation was ignored [5]. In addition, the resulting growth rates are compared with the available literature and it is found that, for a certain range in the model parameters, the agreement is quite satisfactory. This work provides valuable insight into the dominant mechanisms for mass transport as well as morphological evolution and growth of IMC layers during early stages of Pb-free soldering.     

Stabilization and strengthening of nanocrystalline copper by alloying with tantalum

Nanocrystalline Cu-Ta alloys belong to an emerging class of immiscible high-strength materials with a significant potential for high-temperature applications. Using molecular dynamics simulations with an angular-dependent interatomic potential, we study the effect of Ta on the resistance to grain growth and mechanical strength of nanocrystalline Cu-6.5 at.% Ta alloys. Ta segregation at grain boundaries greatly increases structural stability and strength in comparison with pure copper and alloys with a uniform distribution of the same amount of Ta. At high temperatures, the segregated Ta atoms agglomerate and form a set of nanoclusters located at grain boundaries. These nanoclusters are capable of pinning grain boundaries and effectively preventing grain growth. It is suggested that the nanoclusters are precursors to the formation of larger Ta particles found in Cu-Ta alloys experimentally.     

Analysis of grain growth process in melt spun Fe-B alloys under the initial saturated grain boundary segregation condition

A grain growth process in the melt spun low-solid-solubility Fe-B alloys was analyzed under the initial saturated grain boundary (GB) segregation condition. Applying melt spinning technique, single-phase supersaturated nanograins were prepared. Grain growth behavior of the single-phase supersaturated nanograins was investigated by performing isothermal annealing at 700 °C. Combined with the effect of GB segregation on the initial GB excess amount, the thermo-kinetic model [Chen et al., Acta Mater. 57 (2009) 1466] was extended to describe the initial GB segregation condition of nanoscale Fe-B alloys. In comparison of pure kinetic model, pure thermodynamic model and the extended thermo-kinetic model, an initial saturated GB segregation condition was determined. The controlled-mechanism of grain growth under initial saturated GB segregation condition was proposed using two characteristic annealing times (t₁ and t₂), which included a mainly kinetic-controlled process (t ≤ t₁), a transition from kinetic-mechanism to thermodynamic-mechanism (t₁ < t < t₂) and pure thermodynamic-controlled process (t ≥ t₂).     

异种耐热钢瞬时液相扩散连接界面形态与形成机理

采用瞬时液相扩散连接双温工艺对异种耐热钢管进行了连接,使用氩气保护,FeNiCrSiB非晶箔作为扩散连接中间层.研究了异种耐热钢瞬时液相扩散连接界面的形成机理,测试了接头的组织和性能,采用激光共聚焦显微镜研究分析了界面形貌.结果表明,异种钢瞬时液相扩散连接时,液态中间层的结晶过程是在基体上联生生长,晶体长大具有方向性,少量杂质在接头中心以曲线状分布,形成了非直线型的连接界面.双温工艺的短时高温加热过程有利于破碎界面氧化物形成洁净连接晶面层,促进晶粒外延生长.     

预制膜对铝合金微弧氧化陶瓷层生长过程的影响

在磷酸盐体系电解液中,利用微弧氧化技术,分别对有、无高温氧化预制膜的铝合金进行表面陶瓷化处理,研究了预制膜对陶瓷层生长的影响规律.结果表明:高温氧化预制膜有利于提高陶瓷层的生长速率,降低起弧电压;陶瓷层的生长先是以初期形成的陶瓷颗粒为核心呈线状扩展,然后多条线接合呈网状,最后蔓延成面;陶瓷层生长的初期以高温氧化预制膜熔化生成为主,到后期,则是以铝合金基体熔化生成为主,此时预制膜对陶瓷层生长过程的影响较小,但由预制膜生成的陶瓷对陶瓷层生长的影响较大.     

热压工艺对SiCf/Ti复合材料界面反应层生长影响的数值模拟

提出一个热-力-扩散-反应强耦合相场模型来研究热压烧结制备工艺对连续碳化硅纤维增强钛基复合材料中金属间化合物生长规律的影响。模拟结果表明,在两种不同温度下各个界面反应层(Ti₃SiC₂/Ti₅Si₃C_x/Ti₅Si₃C_x+TiC/TiC)的厚度生长与试验值吻合较好。增大外加压力能促进界面层厚度的生长,但对其中抗拉强度最低的Ti₅Si₃层的生长起显著的抑制作用,同时使各界面反应层由周向拉应力状态逐渐转变为压应力。温度的升高使断裂韧度最大的Ti₃SiC₂层厚度增大,但也使总界面层和Ti₅Si₃层的厚度增加。因此,在制备工艺上适当增加压力并选择合适的温度,得到厚度适宜的界面反应层的同时,尽可能使Ti₅Si₃层变薄和Ti₃Si...     

形变组织对水电用高强度贝氏体钢再加热奥氏体晶粒长大的影响

对某水电用800 MPa调质贝氏体高强钢进行了热变形-热处理晶粒长大的实验室联合试验。采用Gleeble-3500热力模拟试验机对钢试样进行不同工艺热压缩变形后冷却至室温,随后对试样进行模拟淬火再加热,在900～1200℃不同温度和保温时间条件下奥氏体化,研究热变形组织的差异对重新奥氏体化晶粒长大的影响规律。结果表明,不同应变速率(0.01～10 s^-1)、变形温度(900～1150℃)和60%工程应变下,试验钢获得的变形组织大致可分为3类：带有明显变形特征的组织、均匀细小的完全再结晶组织和已长大粗化的再结晶组织。3类组织再加热过程中其晶粒长大趋势基本相同,起始晶粒尺寸越大则最终奥氏体晶粒尺寸越大;但在950℃等温时,带有明显变形特征组织的变形试样奥氏体晶粒先缓慢长大后又迅速长大粗化。经评估验证,所建立的Sellars模型、Beck模型和Hillert模型晶粒长大动力学方程对于试验钢的奥氏体晶粒长大行为均有比较满意的预测效果。3类变形组织对应的Hillert模型及Sellars模型中奥氏体长大激活能基本相同,说明同一成分钢种的初始组织的差异并未显著影响晶粒长大机制...     

增材制造GH3536合金的高温拉伸及疲劳裂纹扩展性能研究

采用选区激光熔化技术制备GH3536合金试样,经热等静压和固溶处理后对合金试样的显微组织、高温拉伸性能和不同应力比下的裂纹扩展性能进行了分析。结果表明,经热等静压和固溶处理后合金试样内部存在2种不同大小的等轴晶粒,在晶间存在连续片状分布的M₂₃C₆和M₆C碳化物。合金试样的拉伸性能随着温度的升高而不断下降,断裂方式由室温下的韧性断裂转变为900℃下的脆性断裂。在不同应力比下,合金试样的裂纹扩展方式主要为穿晶扩展,裂纹扩展速率随着应力比的不断上升而提高,在高应力比下合金内部的疲劳裂纹更倾向于在取向差较小的晶粒内部扩展。