Preparation Of Cubic Boron Nitride/Titanium/Aluminum Composites By Spark Plasma Sintering

Cubic boron nitride (cBN) is a well-known superhard material which possesses thehigh hardness only after diamond, the higher thermal stability than diamond and chemicalinertness with ferrous alloys. Therefore cBN has extensive applications in industry.However, as the direct synthesis of cBN monocrystal with jumbo size and high quality isalways difficult, micro-cBN powder and bond are generally sintered to prepare cBN/bondcomposites by high-pressure method. Unfortunately, cBN may transform to thegraphite-like hBN at high sintering temperature. The appearance of hexagonal boronnitride (hBN) will reduce the hardness and bending strength of composites. Although thephase transformation of cBN to hBN could be restrained by a high-pressure method, someinevitable disadvantages such as high cost, limited sample size and complex fabricatingprocess still restrict its application in industry. Therefore, Spark plasma sintering (SPS)has been selected in this paper, SPS can depress the phase transformation of cBN to hBNon account of its high heating rate. Besides, in order to make up the condition withouthigh pressure to restrain the phase transformation of cBN to hBN via SPS, it’s necessaryto further seek for a suitable bond which can absorb hBN generated by cBN.In this paper the Ti-Al bond which has strong reaction capacity with hBN had beenselected to sinter cBN composites via SPS. The main contents are as follows: The relativedensity and the bending strength of each composite were measured by an Archimedesmethod a three-point bending method. The cBN composite sintered by SPS at1400C for10min dwell time under50MPa axial pressures has the highest relative density (98.91%)and the highest bending strength (390.73MPa).Phase structures of composites weredetermined by X-ray diffraction and Raman spectroscopy. The results show the matrix ofcomposites was TiN, TiB2and AlN. It also shows that no hBN phase had been found in thecomposites sintered at1300and1400C, and when the sintering temperature was beyond1500C, the hBN phase was observed in composites.Morphologies of composites weredetermined by field emission scanning electron microscopy. When the sintering temperature was beyond1400C, the composites became dense.And It had been foundthat a transcrystalline fracture occurred at the composite sintered at1400C. The cBNcomposite sintered at1400C possessed the highest relative density and the highestbending strength, and no hBN phase was found in it.