Investigation On Preparation, Microstructure And Properties Of AgTiB₂ Composite

Since the traditional AgCdO electricial contact materials can cause Cd poison during manufacturing process and in service, which is harmful to the environment and human health, and AgSnO2 contact materials have a large contact resistance and high temperature rise that affect the stability and reliability of integral electrical system, they can not meet the increasingly stringent requirements for green environmental protection, longer service life and lower energy consumption. Subsequently, it is of vital engineering and scientific significance to develop a novel Ag-based contact material. In this investigation, a new AgTiB2 composite material were prepared by mechanical alloying and powder metallurgy. The effect of milling time on the morphology, size and distribution of milled powders, and the effect of processing parameters, such as sintering temperature, compatibility, TiB2 content, repressing and resinter-ing and the additives (WO3, CuO and BiO3) on the microstructure and properties of AgTiB2 composite was studied systematically. The arc erosion characteristics of the composite material were evaluated as well. The following conclusions can be drawn from this investigation:1. At a ball-to-mass ratio of 60:1, the morphology of AgTiB2 compound powders is evolved from coarse flakes to fine particles, followed by coarsening with increasing the milling time. The finest and well-dispersed powders with an average size of 1.9μm can be obtained at 60h. Sintering temperature has a significant effect on the physical properties of AgTiB2 composites, and the hardness and electrical conductivity have a tendency to decrease and then increase, followed by decreasing. With increasing temperature the high compaction can contribute to the improvement of the hardness for Ag TiB2 composite, but deteriorate the electrical conductivity.2. The increase in TiB2 content results in a low relative density and serious agglomerations of TiB2. Repressing and resintering process favor the densification and the increases in the good combination of properties. In comparison with Ag-0.13wt%TiB2 without repressing and resintering, the density, hardness and electrical conductivity increase from 7.2454g/cm3, 55.6HV and 32.78%IACS to 7.9112g/cm3,90.0HV and 51.7%IACS after repressing and resintering.3. CuO addition has no obvious effect on the properties of AgTiB2 while Bi2O3 addition can increase the densification. Among three additives, WO3 addition has the best effect to enhance the densification and uniformity, In comparison with AgTiB2 without any addition, the density, hardness and electrical conductivity are increased by 8.6%,10% and 47%, respectively.4. AgTiB2 composite with 0.13wt% TiB2 present a serious arc erosion and deep erosion pits on the surface while the erosion pits become much smaller and shallower at 0.5wt%TiB2. However, arc erosion aggravates with further increased TiB2 content. It suggests that an appropriate TiB2 content can disperse arc effectively. Moreove, WO3 addition can enhance the arc erosion resistance of Ag-1.0wt%TiB2 composite.