Control Of The Microstructure And Performance Of Nano-aln Modified Low Temperature Vitrified Diamond Tools

Vitrified bond diamond grinding tool is the most ideal tools for high speed andprecision grinding machining, the performance control of the bonds for vitrified bonddiamond grinding tools is always a research focus.In this thesis, the three pre-fritted glass of R₂O-B₂O₃-SiO₂（RBS）, R₂O-Al₂O₃-SiO₂（RAS） and R₂O-Al₂O₃-B₂O₃-SiO₂（RABS） were designed based on the performancerequirements of low temperature vitrified bond for diamond grinding tools, furthermore,the performance of the three vitrified bonds were investigated, and then the optimumpre-fritted glass were optimized. On this basis, the effects of the nano-AlN and sinteringatmosphere on the performances of the nano-AlN modified vitrified bonds and thediamond grinding tools were studied, and the effect of the porosity on the grindingperformances of the diamond tools for machining PCD tools, then the nano-AlN modifiedvitrified bond diamond grinding tools with high performances for machining PCD toolswere prepared.The RABS pre-fritted glass with amorphous phase and a little crystal phase has agood wettability with diamond, the range of sintering temperature is from680to715°C,the linear expansion coefficient is about5.5861×10-6°C-1, the bending strength is65MPa,and the microhardness is693MPa. Therefore, the RABS pre-fritted glass is very suitablefor preparation the vitrified bond diamond grinding tools.Addition of nano-AlN in pre-fritted glass can increase the strength, hardness andwearability, and decreases the linear expansion coefficient. The optimum added amount is6wt.%. As sintering in argon atmosphere and addition of6wt.%nano-AlN, the bendingstrength of the vitrified bond can reach to70.8MPa, the impact strength can reach to12.3kJ m^-2, the hardness can reach to810MPa. The nano-AlN with high surface activitypromotes the crystallizing, increases the amount of crystal phase, and refines the grain sizeof crystal phase, simultaneously, modifies the morphology of pores during sintering inargon atmosphere, furthermore, improves the performances of vitrified bonds. However,during sintering in air, the beneficial effects decrease because of the nano-AlN oxidativedecomposition, which results that the performances of bond sintered in air are lower than in argon atmosphere.The diamond tools with the nano-AlN modified vitrified bond were prepared. Thelower linear expansion coefficient and good wettability with diamond increase thebonding force between the vitrified bonds with diamond. The performances of diamondtools are nearly same as to the the vitrified bonds. As sintering in argon atmosphere andaddition of6wt.%nano-AlN, the bending strength, hardness and impact strength ofnano-AlN modified vitrified bond diamond tools reach to60.8MPa、HRB88and10.32kJ/m², respectively. Which are high than vitrified bond diamond tools by25.2%,63.0%and16.9%, respectively.Addition of pore-forming agent in the nano-AlN modified vitrified bond diamondgrinding wheels can control the amount, the distribution and the size of pores due to thegas came from pore-forming agent decomposition and its overflow from wheels duringsintering process. The small and closed pores distributed in band bridges decrease. Thepores connect with each other, forming a perfect network of pores in the wheels, whichcan efficiently arrest crack propagation, accelerate the removal of the chippings, and aidcooling fluid flow on the abrasive surface. Furthermore, the impact strength, grindingefficiency, self-dressing, service life of the wheels and the surface roughness of the workpieces are improved. The optimum porosity of the nano-AlN modified vitrified bonddiamond grinding wheels for grinding PCD tools is40.5vol.%in this work.