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首页> 外文学位 >High-pressure, high-temperature sintering of polycrystalline cubic boron nitride with improved thermostability and mechanical properties for high temperature applications.
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High-pressure, high-temperature sintering of polycrystalline cubic boron nitride with improved thermostability and mechanical properties for high temperature applications.

机译：对高温应用具有改善的热稳定性和机械性能的多晶立方氮化硼多晶进行高压高温烧结。

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摘要

Polycrystalline cubic boron nitride (PCBN) is one of the few materials suitable for friction stir welding (FSW) of hardened steels, which demands tool materials to possess high temperature strength, toughness, abrasion resistance, thermal and chemical stabilities.;In FSW process at temperatures higher than 980°C PCBN consisting of AlB2, as one of the major reaction products, underwent a reverse peritectic reaction: AlB2 → Al(l) + AlB 12 and released liquid Al, which was believed to cause inter-cBN granular cracking in the PCBN tool during FSW of hardened steel.;In the present research, PCBN starting with decreased Al additive and addition of fine cBN powder, was HP/HT-sintered at higher B:Al ratio and increased available BN surface area for fast in situ reaction with liquid Al in favor of forming AlB12 instead of AlB2. Titanium powder in HP/HT-sintering of PCBN under the same pressure and temperature conditions resulted in cBN, TiN, and TiB2 reaction products but could not achieve the densification comparable to the Al additives. However, using Ti-coated cBN particles with addition of the fine cBN powder led to PCBN with highly packed reaction products of cBN, TiN, and TiB2 and strong mechanical properties.;Applying electron backscattered diffraction (EBSD) method, the PCBN with 10vol%Al additive was detected to consist of 0.5vol% and finely dispersed AlB2 in addition to AlB12 as the major borides in addition to cBN and AlN. Such PCBN was shown to possess high thermostability measured at 1000°C and measureable increases in flexural strength at temperatures up to 1100°C, while room temperature fracture toughness value was retained up to 1100° C as well. Combine x-ray diffraction (XRD) and EBSD results revealed the increase in high-temperature strength was resultant of high residual compressive-stress on cBN grains applied by thermal expansion of the AlN-AlB 12 grainboundary phase. The PCBN sintered from cBN with 10vo%Al powder, possessing improved thermostability and mechanical strength at temperatures up to 1100°C benefiting from significantly reduced AlB2 and increased cBN vol%, is suitable for high temperature applications. The PCBN sintered using the Ti-coated cBN particles showed significant decrease in strength and toughness measured in 900°C to 1100°C range, due to oxidation reactions of TiN and TiB2 at high temperatures.
机译：多晶立方氮化硼（PCBN）是少数几种适用于淬硬钢的摩擦搅拌焊（FSW）的材料之一，它要求工具材料具有高温强度，韧性，耐磨性，热和化学稳定性。在高于980°C的温度下，由AlB2作为主要反应产物之一的PCBN经历了反向包晶反应：AlB2→Al（l）+ AlB 12并释放出液态Al，据信这引起了cBN间的晶粒间裂在本研究中，以较高的B：Al比和增加的可用BN表面积进行HP / HT烧结，从减少Al添加剂和添加精细的cBN粉末开始的PCBN工具，以实现快速原位成型。与液态Al反应，有利于形成AlB12而不是AlB2。在相同的压力和温度条件下，PCBN的HP / HT烧结中的钛粉会生成cBN，TiN和TiB2反应产物，但无法实现与Al添加剂相当的致密化。但是，使用Ti包覆的cBN颗粒并添加细的cBN粉末会导致PCBN具有cBN，TiN和TiB2的高度堆积的反应产物，并且具有很强的机械性能。;采用电子背散射衍射（EBSD）方法，PCBN的含量为10vol％除了cBN和AlN之外，还检测到Al添加剂由0.5vol％的AlB2和除AlB12以外的细分散的AlB2组成。这种PCBN在1000°C时具有很高的热稳定性，在高达1100°C的温度下弯曲强度也有可测量的增加，而在1100°C时仍能保持室温断裂韧性值。结合X射线衍射（XRD）和EBSD结果表明，高温强度的增加是由于AlN-AlB 12晶界相的热膨胀对cBN晶粒造成的高残余压应力的结果。由cBN与10％（体积）Al粉末烧结而成的PCBN，由于AlB2的明显减少和cBN体积％的增加，在高达1100°C的温度下具有改善的热稳定性和机械强度，适用于高温应用。由于TiN和TiB2在高温下的氧化反应，使用Ti涂层的cBN颗粒烧结的PCBN在900°C至1100°C范围内测得的强度和韧性显着降低。

著录项

  • 作者

    Yao, Xian.;

  • 作者单位

    The University of Utah.;

  • 授予单位 The University of Utah.;
  • 学科 Materials science.
  • 学位 Ph.D.
  • 年度 2014
  • 页码 205 p.
  • 总页数 205
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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