摘要
用二元共晶相图对等温凝固过程中固相内溶质 (MeltingPointDepressant )浓度分布及等温凝固产物进行了定性理论分析 ,指出 :固相区在焊接温度下的“饱和浓度”仅会出现在液 -固界面固相侧 ,故等温凝固进程受控于固相中扩散的原因在于溶质原子在固相中存在浓度梯度 ;等温凝固结束后虽在焊接温度下可获得固溶体 ,但冷至室温时可能会有化合物相脱溶析出。在此基础上 ,介绍了等温凝固过程的四种解析解法———薄膜解、单相解、双相解、单 -双相混合解及其优缺点。其中后三者的共同求解规律是基于固相内浓度分布方程与物质守恒方程进行求解的 ,它们的差别主要来自于在处理固 -液界面的移动对固相内浓度分布的影响时采用了不同的方法。总结了液相区最大宽度的影响因素 ,并给出两种基于物质守恒定律估算液相区最大宽度的方法。各解析解均存在未考虑压力与晶界作用的不足。
With a typical binary eutectic phase diagram,the solute (MPD:Melting Point Depressant) concentration distribution in solid phase during isothermal solidification stage and the products after isothermal solidification in transient liquid phase (TLP) bonding process are qualitatively analyzed in principle.The saturated solute concentration in solid phase is at liquid/solid interface at bonding temperature,and it is a constant,so a solute concentration gradient exist in solid,therefore it is point out that the isothermal solidification is controlled by solute diffusion in solid.The products after isothermal solidification will be solid solution at bonding temperature, although other phase will precipitate at room temperature. In addition,four types analytical solutions for isothermal solidification stage in TLP bonding process,namely thin film solution,single-phase solution, two-phase solution and a solution combined single-phase solution and two-phase solution,and their merits or demerits are also introduced.The after three solutions are derived all by applying the mass conservation equation and the solute concentration distribution equation in solid phase.It is worth emphasizing that the reasons for difference between them is that treating the influence of the moving liquid/solid interface on the solute concentration distribution in solid phase in different ways.The factors to influence maximum width of the molten zone are summarized, and two equation for estimation of the maximum width of the molten zone are given by the mass conservation principle.The effects of pressure and grain boundary on solute diffusion are not consider in any above solution.
出处
《焊管》
2004年第6期25-31,87-88,共7页
Welded Pipe and Tube
