Chemical Performance Match Between Cemented Carbide Tools And Ti-6Al-4V Alloy

Titanium alloy is well known as a typical difficult-to-machine material because of its low thermal conductivity, high chemical reactivity, low modulus of elasticity and high friction factor with other metal materials. This paper selected the wear mechanism of cutting tools in high-speed machining titanium alloy as an entry point, through theory analysis and experiment research, simulated the dissolution-diffusion process between cemented carbide tools and work-piece, systemically investigated the chemical performance matching relationship between cemented carbide tools and titanium alloy. At last, oxidation wear and dissolution-diffusion wear of different carbide tools were validated and analyzed through milling titanium alloy experiments, the chemical properties matching relationship were set up between carbide tools and titanium alloy, providing reliable bases for choosing suitable carbide tools in high-speed machining titanium alloy.Based on the thermodynamic theory of dissolubility, the solubility of WC, TiC and Co in Ti were calculated. The solubility of WC, TiC and Co in Ti were greatly effected by temperature, and the solubility in Ti increased as the temperature increased. Expression of element diffusion concentration and expression of diffusion flux that adapt to carbide tools and titanium alloy were obtained through Fick's laws of diffusion analysis. Further more, based on the expression of element diffusion concentration, we got the method for calculating diffusion coefficients between carbide tools and titanium alloy, accordingly provided theoretical foundation for explaining and analyzing diffusion experiments logically. We also made primary discussion about microscopic mechanism in element diffusion between carbide tools and titanium alloy.Thermodynamic calculation of oxidation reaction between carbide tools and titanium alloy was got using Gibbs-Free Energy function, then oxidation reaction possibility and reaction products were analyzed theoretically. The results showed that at a temperature of 1000 K oxidation reaction would took place between carbide tools and titanium alloy in the air, WC, TiC and Co in carbide tools were oxidated into WO3, Co3O4 and TiO2 respectively, Ti, Al, and V in titanium alloy were also oxidated into corresponding oxidation products, Ti in titanium and WC in carbide tools turned into TiC and W through displacement reaction.Five carbide tools of YT5, YT15, YG6, YG6X and YG8 were chosen for element diffusion experiment with Ti-6Al-4V, element diffusion of different carbide tool materials with Ti-6Al-4V under the same diffusion condition was analyzed in detail, and the diffusion effect between tool material and workpiece material caused by diffusion temperature and diffusion time was reviewed systemically. The results showed that under the same condition, element diffusion of YT carbide tool materials with Ti-6Al-4V was serious than YG, YG carbide tool materials containing more Co had a more serious diffusion degree, and fine grain tool materials had a little diffusion with Ti-6Al-4V; dissolution-difusion degree between Ti-6Al-4V and the five carbide tools were as follows:YT15>YT5>YG8>YG6>YG6X; diffusion temperature greatly effected element diffusion, diffusion degree between carbide tools and titanium alloy increased as temperature increased; diffusion degree also increased as diffusion time increased, and reached a stable state after about 1.5 h, then it hardly increased even extend diffusion time.Tool hardness was tested after diffusion experiment, and the results showed that there was nearly no changes in tool hardness that carried no diffusion, but tool hardness that had carried diffusion greatly changed, hardness near the diffusion interface obviously decreased compared with normal tool hardness, and hardness far away form the interface reached a normal level gradually. Although it is only several microns took place between tool material and titanium alloy, the effect caused by diffusion was more than several tens of microns.Antioxygenic property of different tool materials was systemically analyzed by oxidation experiment using five carbide tools. Results showed that oxidation reaction of carbide tool materials took place when temperature reached 800 K, WC in tool materials was partly oxidated into WO3, and Co was oxidated into Co3O4 in the temperature of 900 K, TiC in tool materials was found oxidated into TiO2 when the temperature reached 1300 K, antioxygenic property of YT was better than YG, the main factor effect carbide tool oxidation was grain size when components and content were nearly the same, the smaller of the grain size, the better antioxygenic property. Through the oxidation reaction experiment of Ti-6A1-4V, we found that oxidation reaction took place at the temperature of 1100 K, Ti reacted with O2 and N2 in the air and resulting into TiO2 and Ti4N3.Milling experiment of Ti-6AI-4V was done under the same cutting parameters, and the results showed that wear degree of YT carbide tools was far more than YG carbide tools, dissolution-diffusion wear and oxidation wear were the main wear mechanism; the oxidation wear degree of the five carbide tools were as follows:YT15>YT5> YG6>YG8>YG6X; during the progress of cutting, titanium alloy chipping was clearly found bonded on tool surface, and made element diffusion easily took place with tool materials, dissolution-diffusion degree of the five carbide tools were as follows:YT15>YT5>YG8>YG6>YG6X.The chemical performance matching relationship between the five different carbide tools and Ti-6A1-4V was investigated through theory analysis and experiment research, and we concluded that:dissolution-diffusion degree of YG fine grain carbide tool was the least; YG fine grain tool had a smallest dissolution-diffusion wear and oxidation wear during practical cutting, so YG fine grain carbide tool material had a best chemical matching with Ti-6Al-4V.