Microstructure,thermodynamics and compressive properties of AlCrCuNixTi (x = 0, 1) high entropy alloys

Two equiatomic high entropy alloys, AlCrCuNi_xTi (x?=?0, 1), were prepared by an arc furnace. Their microstructure, thermodynamics and compressive properties were investigated in as-cast state. The AlCrCuTi alloy consists of a face centred cubic (fcc) phase, two body centred cubic (bcc) phases and an Al₄Cu₉-like phase, while the AlCrCuNiTi alloy contains an fcc phase and two bcc phases. Thermodynamic expressions based on mixing enthalpy matrix facilitate the thermodynamic calculation. The element Cr takes severe segregation during solidification and forms Cr rich phases in both alloys. The addition of Ni to the AlCrCuNiTi alloy inhibits the formation of intermetallic compounds and enhances the yield strength, compressive strength and ultimate strain, but degrades Vickers hardness.     

Diffusion bonding of TiAl based alloy to Ti–6Al–4V alloy using amorphous interlayer

Powder metallurgical TiAl based alloy and Ti–6Al–4V (TC4) alloy were diffusion bonded at 915 °C for 1 h under a pressure of 80 MPa. Single Ti‐based amorphous or Ni‐based amorphous foil was utilized as an interlayer during diffusion bonding process. The tensile mechanical properties of the diffusion bonded joints between TiAl based alloy and TC4 alloy were tested. The fracture surface and microstructure characteristic of these joints were also observed carefully by scanning electron microscope. The TiAl based alloy with a fully lamellar microstructure is more suitable for diffusion bonding to TC4 alloy. Adding a Ti‐based amorphous interlayer is more conducive to the element diffusion, giving rise to the improvement in the mechanical properties of the diffusion bonded joints. Results also show that the diffusion bonded joints form a metallurgical bond and fracture in a brittle manner.     

基于多维有限自动机的DFA改进算法

多个正则表达式规则编译成一个DFA(deter minister finite automata)时,会产生状态爆炸、存储急剧增加的现象。针对最严重的状态爆炸问题,从信息论的角度给出了解释,并提出多维数学模型,将冗余状态分为0维状态和1维状态,通过前者按照维度压缩,后者动态构建的方法将空间复杂度降到理论下界,并在此基础上提出多维有限自动机(MFA, multi-dimensional finite automata)。实验表明,MFA构造时间比XFA略少,比DFA、STT冗余压缩算法和Hybrid-FA降低了2~3个数量级;存储空间比XFA略高,比DFA、STT冗余压缩算法、mDFA、Hybrid-FA降低了1~2个数量级;匹配时间比DFA、Hybrid-FA略多,但是比XFA略少,比STT冗余压缩算法和mDFA降低了1~2个数量级。