Theoretical Calculation And Experimental Investigation Of The Surface Tension Of(Ti,Zr,Hf,Si)Multi-Alloy Melts

High-temperature alloys are introduced into C/C composites by reactive melt infiltration（RMI）and react with the pre-deposited matrix to form ultra-high-temperature ceramics,which is one of the most important methods to improve the ablation resistance of C/C composites.Currently,the modification of C/C composites by the RMI process using a multi alloy consisting of transition group metals such as Hf,Zr,Ti and Si is becoming a new trend in the domain of high temperature composites research.Surface tension,as a fundamental thermophysical parameter of the alloy melt,has an important influence on the infiltration of the alloy melt into the microporosity of C/C composites.Therefore,in this work,the surface tension of the above-mentioned multi alloy melt was measured by the suspended drop method at 1773-2173 K.The Butler theoretical model was used to calculate the surface tension of the alloy melt.By comparing the experimental measurements with the calculated values,the variation of the surface tension of the alloy melt with component and temperature was obtained,and the main conclusions are as follows.（1）The difference between the measured and calculated surface tensions of binary（Ti-Zr,Ti-Hf,Si-Ti,Si-Zr and Si-Hf）and ternary（Ti-Zr-Hf,Si-Ti-Zr,Si-Ti-Hf and Si-Zr-Hf）alloys is only in the range of 0.3%to4.8%,with a very good agreement between the experimental measurements and the theoretical calculations,indicating that the Butler model can be applied to the calculation of surface tensions of binary and ternary alloys of high melting point transition group metals.（2）The surface tension of Ti-Zr,Ti-Hf binary and Ti-Zr-Hf ternary alloys showed a similar linear increase with the increase of Zr or Hf content;while the surface tension of Si-containing binary and ternary alloys showed an increase followed by a decrease with the increase of Ti,Zr or Hf content.（3）The surface tension of the Ti_0.142Hf_0.189Zr_0.568Si_0.1 quaternary melt was 1538,1511 and 1496 m N/m at 1873 K,1973 K and 2073 K,respectively.At the same temperature,the surface tension of the Ti-Zr-Hf-Si quaternary melt decreased with increasing Si content.At 2073 K,Ti:Hf:Zr:Si=3:4:12:,the surface tension decreased from 1515 m N/m to1486 m N/m when the molar fraction of Si（）was increased from 0.05 to0.15.（4）For alloys with infinite solid solution（Ti,Zr and Hf）,the surface tension of the alloy increases linearly with the addition of high surface tension Zr or Hf components,while for Si-containing multi-alloy systems,the presence of short-range ordered Si-Ti,Si-Zr or Si-Hf clusters in the alloy melt reduces the surface tension and eventually leads to a non-linear trend in the surface tension of the multi-alloy system.（5）The volatilization of low melting point components（Si or Ti）under high vacuum test conditions leads to a change in the alloy composition,i.e.a relative increase in the content of high melting point（high surface tension）components,resulting in a slight increase in the surface tension of the alloy;while the introduction of a small amount of C impurity phase,and its segregation on the melt surface reduces the surface tension of the alloy;the difference between the experimental and calculated values of the alloy surface tension in this study is mainly due to the combined effect of these two factors.