超细硬质合金高温处理表面氧化行为及对合金性能的影响

Surface Oxidation Behavior of Ultrafine Cemented Carbides after High-Temperature Treatment and its Effect on Alloy Properties

将4种常用高性能超细硬质合金棒材分别在空气、低真空中,加热至300~1000℃并保温不同时间,研究了高温处理的表面氧化行为及其对合金性能的影响。结果表明:在空气氛围中,在400℃及以下时,超细合金未见氧化,在500℃及以上时,合金发生明显氧化,表面明显变得粗糙,最终完全氧化;在低真空氛围中,温度为600℃及以上时,合金发生氧化,氧化层较薄。在空气中,加热到500℃时,出现CoWO_(4)和WO_(3)相;随着保温时间由30 min延长至120 min,氧化层厚度增加,CoWO_(4)和WO_(3)占比逐渐增加;加热到800℃时,CoWO_(4)和WO_(3)占比趋于稳定,合金表面已完全氧化。超细硬质合金抗氧化能力随合金钴相平均自由程增加而增强,钴相比表面积越大,越容易被氧化成CoWO_(4)。由于CoWO_(4)和WO_(3)体积膨胀,形态疏松,氧气顺着蓬松的氧化层渗入,导致合金氧化加剧。随着氧化进行,合金矫顽磁力、钴磁及硬度未发生明显变化,合金横向断裂强度下降。去除氧化层后,合金横向断裂强度与未氧化时相当,这表明合金加热氧化后横向断裂强度的降低主要是表面氧化所致。氧化后的样品去除氧化层后制作成精密微型钻头和铣刀,其使用寿命与未氧化时相当。

The surface oxidation behavior and effect on alloy properties of Four commonly used high-performance ultra-fine cemented carbide rods were studied by heating them in air and low vacuum to 300~1000℃and holding them for different time.The results show that in an air atmosphere,there is no oxidation observed in ultra-fine alloys at temperatures below 400℃.However,at temperatures above 500℃,the alloy undergoes significant oxidation,with the surface becoming noticeably rough and ultimately completely oxidized.In a low vacuum atmosphere,when the temperature is 600℃or above,the alloy undergoes oxidation,and the oxide layer is relatively thin.When the alloy is heated to 500℃in the air,CoWO_(4)and WO_(3)phases appear.As the holding time increases from 30 minutes to 120 minutes,the thickness of the oxide layer increases,and the proportion of CoWO_(4)and WO_(3)gradually increases.When the alloy is heated to 800℃,the proportion of CoWO_(4)and WO_(3)tends to stabilize,and the alloy surface has completely oxidized.The oxidation resistance of ultra-fine cemented carbide increases with the cobalt mean free path,and a larger surface area of cobalt indicates that it is easier to be oxidized into CoWO_(4).Due to the volume expansion and loose morphology of CoWO_(4)and WO_(3),oxygen infiltrates through the fluffy oxide layer,leading to intensified alloy oxidation.As oxidation progresses,there is no significant change in the coercive force,cobalt magnetism,and hardness of the alloy,and the transverse rupture strength of the alloy decreases.After removing the oxide layer,the transverse fracture strength of the alloy is equivalent to that without oxidation,indicating that the decrease in transverse fracture strength of the alloy after heating and oxidation is mainly caused by surface oxidation.After removing the oxide layer from the oxidized sample,the alloy is made into precision micro drills and milling cutters,with a service life comparable to that before oxidation.