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.
Phase formation during mechanical alloying in the Ti–Si system
Abstract Mechanical alloying of Ti–Si powder mixture or TiH 1.924 –Si powder mixture was performed by high-energy ball milling, in which the Ti to Si mole ratio was 1:2. The phase formations in both mixtures during milling were investigated by X-ray diffraction. Mechanical alloying a mixture of elemental powders led to the formation of TiSi 2 equilibrium compound, while when starting from Si + TiH 1.924 , a metastable phase was formed. The metastable phase completely transforms to TiSi 2 when the mechanically alloyed powder is annealed at temperatures above 800 °C. Two different pathways of phase transitions during mechanical alloying are attributed to the existence of hydrogen atoms, i.e., when starting from Si + TiH 1.924 compared to Si + Ti, the kinetics for the formation of the TiSi 2 intermetallic compound slows down. The kinetics related to the different phase transitions depending on the starting powder mixture are discussed.