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本研究在保证碳化硼粉末充分热致密化的前提下,控制了晶粒长大,从而获得了高强度的微晶碳化硼制件。研究中采用硼酸碳热还原法在碳管炉中制得碳化硼粗粉,经振动球磨、酸洗和分级获得了微米级细粉,其化学成分和杂质含量符合国标GB5151-85中PB_4CH-1粉末的要求。本研究还进行了添加剂对热压碳化硼晶粒长大影响的实验。实验表明:硼的加入不仅降低了热压温度,而且有效地控制了晶粒长大,用同种粉末和工艺,晶粒度由6.00μm降至3.72μm。在普通烧结中,少量碳的加入显示了很好的烧结活化作用,但碳对热压没有显示积极的效果。氧化钐的加入明显促进晶粒长大,在相同条件下,晶粒度高达8.06μm。本研究制得的成品由于充分保证了热致密化,故其热压坯晶界强度高,断口晶粒细且均匀,抗弯强度与晶粒度之间的关系符合Osipov建立的方程:σ=σ_0+Kd~(-1/2)。其性能达到或超过了文献报导的最好水平。主要性能为:抗弯强度:578-585MPa;克努普硬度(负荷100g):2800—3000km/mm~2;孔隙度:<0.5％;平均晶粒度:1—2.5μm;比重:2.49—2.51g/cm~3。
In this study, under the premise of fully thermal densification of boron carbide powder, the grain growth was controlled and the high strength microcrystalline boron carbide parts were obtained. In the study, boric acid carbothermal reduction method was used to prepare boron carbide powder in a carbon tube furnace. Micronized fine powder was obtained by vibration ball milling, pickling and grading. The chemical composition and impurity content of the powder complied with PB_4CH-1 of GB5151-85 Powder requirements. In this study, the effect of additives on the growth of hot-pressed boron carbide grains was also studied. Experiments show that boron addition not only reduces the hot pressing temperature but also effectively controls the grain growth. With the same powder and process, the grain size decreases from 6.00μm to 3.72μm. In ordinary sintering, the addition of a small amount of carbon shows good sintering activation, but carbon shows no positive effect on hot pressing. The addition of samarium oxide obviously promotes the grain growth. Under the same conditions, the grain size is as high as 8.06μm. The finished product obtained in this study, due to sufficient thermal densification, has a high strength of hot-pressed blank grain boundaries and a fine and even grain fracture. The relationship between bending strength and grain size is in accordance with Osipov’s equation: σ = σ_0 + Kd ~ (-1/2). Its performance meets or exceeds the best reported in the literature. The main properties are: flexural strength: 578-585MPa; Knud hardness (load 100g): 2800-3000km / mm ~ 2; porosity: <0.5%; average grain size: 1-2.5μm; 2.51g / cm ~ 3.