Effect of a titanium nitride interlayer on the densification, properties and microstructure of cermets based on alumina and nickel — Part 2: Microstructures
SEM microstructural analyses in conjunction with EDX and TEM microstructural analyses have been conducted with cermets based on nickel and alumina, the latter as such and with a chemical-vapour-deposited titanium nitride layer. It has been proved that there is excellent bonding at both the Al2O3/TiN and the TiN/Ni interface, whereas Al2O3 and Ni do not adhere to each other. This is the reason for the observation that the mechanical properties as well as the densification of cermets consisting of Al2O3 and Ni are enhanced by applying a TiN interlayer between the ceramic phase and the metallic phase.
Effect of a titanium nitride interlayer on the densification, properties and microstructure of cermets based on alumina and nickel — Part 1: Densification and properties
In order to manufacture cermets based on Al2O3 and Ni, Al2O3 particles were first coated with TiN by CVD and then mixed with pure Ni powder. The cermets were produced from the mixed powders by powder metallurgy processes. The relative density and the mechanical properties of the cermets are improved due to the presence of the TiN interlayer. The contribution of this interlayer to the mechanical properties of the cermets produced by hot-pressing is superior to that by pressureless sintering.
Rapid rate sintering of Al sub 2 O sub 3 -TiC composites for cutting-tool applications
An earlier study demonstrated that a >97% dense, fine-grained composite of alumina and titanium carbide can be produced by a novel cold press and sintering process which utilizes a rapid heating rate. The barrier to pressureless densification of alumina-TiC, which is overcome by rapid rate sintering appears to be the evolution of gaseous reaction products. The heating rate required to produce densities >95% of theoretical, however, resulted in thermal fracture during rapid heating of green compacts which were designed to produce cutting tool inserts {approx} 1 cm in diameter by 0.5 cm thick. The present study describes the development of means for preventing thermal cracking of even larger specimens. Processing conditions are described for achieving near full density with zero open porosity which permits final densification by containerless hot isostatic pressing. The possibility of enhancing densification by controlling the sintering environment was also investigated. Properties and machining performance of rapid rate sintered alumina-TiC cutting tool inserts were measured and compared with those of commercially hot-pressed material of similar chemical composition.