1) Alloying matrix
In SiC-Al system, Si and Mg are added in Al matrix, as well as the utilization of N2 atmosphere facilitates pressureless infiltration. In SiC-Cu system, pressureless infiltration is realized through the addition of Fe, Ni, Cr and Al [12]. Pressureless infiltration has not been realized in C/metal and diamond/metal composites by alloying matrix, which is still an interesting subject in the future.
2) Activation of ceramic perform
Introducing activator elements (Ti, Cr) in SiC or diamond preforms is beneficial to the decrease of interfacial energy and the enhancement of wettability, resulting in pressureless infiltration of Cu alloy [13 and 30]. But the agglomeration of Ti on the interface degrades TC greatly due to the formation of TiC and Ti-Cu compounds. TC of C/metal and diamond/metal composites is more sensitive to interfacial resistance in comparison with SiC/metal composites [31]. It is important to control the thickness of segregation layer and the degree of interfacial reaction. Modifying reinforcement assures homogeneous distribution of activator elements. Cr-coated diamond and Ti-coated diamond are produced by slow vapor deposition in vacuum or salt bath method, which is approved to be able to successfully improve the wettability.