The in situ formation of TiB 2 particulates via an interface reaction between Ti and FeB powders was studied. The effects of mechanical activation by high-energy milling on the decomposition of TiH 2 and the interface reactions between Ti and FeB powders to form TiB 2 were investigated. Powder mixtures were fabricated using planetary ball-milling under various milling conditions. The specific ball-milling energy was calculated from the measured electrical power consumption during milling process. High specific milling energy (152.6 kJ/g) resulted in a size reduction and homogeneous dispersion of constituent powders. This resulted in a decrease in the decomposition temperature of TiH 2 and an increase in the formation reaction of TiB 2 particulates in the Fe matrix, resulting in a homogeneous microstructure of nanoscale TiB 2 evenly distributed within the Fe matrix. In contrast, the powder mixture milled with low specific milling energy (36.5 kJ/g) showed an inhomogeneous microstructure composed of relatively large Fe-Fe 2 B particles surrounded by a thin layer of Fe-TiB 2 within a finely dispersed Fe-TiB 2 matrix region.

In this study, Fe-40wt% TiB 2 nanocomposite powders were fabricated by two different methods: (1) conventional powder metallurgical process by simple high-energy ball-milling of Fe and TiB 2 elemental powders (ex-situ method) and (2) high-energy ball-milling of the powder mixture of (FeB+TiH 2 ) followed by reaction synthesis at high temperature (in-situ method). The ex-situ powder was prepared by planetary ball-milling at 700 rpm for 2 h under an Ar-gas atmosphere. The in-situ powder was prepared under the same milling condition and heat-treated at 900 o C for 2 h under flowing argon gas in a tube furnace to form TiB 2 particulates through a reaction between FeB and Ti. Both Fe-TiB 2 composite powder compacts were sintered by a spark-plasma sintering (SPS) process. Sintering was performed at 1150℃ for the ex-situ powder compact and at 1080℃ for the in-situ powder for 10 minutes under 50 MPa of sintering pressure and 0.1 Pa vacuum for both processes. The heating rate was 50 o /min to reach the sintering temperature. Results from analysis of shrinkage and microstructural observation showed that the in-situ composite powder compacts had a homogeneous and fine microstructure compared to the ex-situ preparation, even though the sintered densities were almost the same (99.6 and 99.8% relative density, respectively).

40wt% TiB 2 nanocomposites were fabricated by mechanical activation and spark-plasma sintering of a powder mixture of iron boride (FeB) and titanium hydride (TiH 2 ). The powder mixture of (FeB, TiH 2 ) was prepared by high-energy ball milling in a planetary ball mill at 700 rpm for 3 h followed by spark-plasma sintering (SPS) at various conditions. Analysis of the change in relative sintered density and densification rate during sintering showed that a self-propagating high-temperature synthesis reaction occurs to form TiB 2 from FeB and Ti. A sintered body with relative density higher than 98% was obtained after sintering at 1150°C for 5 and 15 min. The microstructural observation of sintered compacts with the use of FE-SEM and TEM revealed that ultrafine particulates with approximately 5 nm were evenly distributed in an Fe-matrix. A hardness value of 83 HRC was obtained, which is equivalent to that of conventional WC-20 Co systems.