【作者】 岳喜山；

【导师】 孙凤莲；

【作者基本信息】 哈尔滨理工大学 ， 材料加工工程， 2005， 硕士

【摘要】 硬质合金具有高硬度、耐高温、抗腐蚀、耐磨损性好等优点,广泛应用于阀门、钻机等的密封装置、各种金属切削工具以及制造各种模具、量具和耐磨损机械零件等,并收到了显著的效果。但由于这些材料塑性、韧性、抗冲击性都较差,在与其他材料钎焊冷却过程中常会因材料的性能参数的不匹配而使接头处产生相当大的残余应力变形甚至产生裂纹,对于大面积硬质合金圆环,钎焊过程中更容易出现裂纹或开裂。为此,对硬质合金与其他材料钎焊后残余应力大小及分布进行预测具有一定的理论和实际意义。 本论文通过采用Marc非线性有限元软件,采用热弹塑性有限元方法,在考虑了材料性能参数随温度变化的情况下,对硬质合金圆环和钢体钎焊的接头区在冷却过程中的应力变化、应力分布及裂纹敏感区等进行了分析。并用微区X射线衍射法对接头附近的残余应力进行了测量以验证模拟的可靠性。 模拟结果表明:在焊后冷却过程中产生的轴向应力,周向应力对接头的强度影响较小,径向应力是接头破坏的主要因素。在钎缝与硬质合金一侧接触面上所受到的残余应力最大,在离硬质合金环内侧 0.4mm处径向拉应力达到最大,在环内侧轴向拉应力最大,在硬质合金环与钎缝一侧接触面的靠近中心侧区域为最危险区域。 研究了钎焊接头形状、钎缝厚度、缓冲层、钎焊压力及构件的尺寸对焊后接头残余应力的影响,结果表明:在钢基体表面开工艺槽时,由于槽的拘束作用,焊后的残余应力与不开工艺槽相比都大大增加,从而对接头的强度不利;随着钎缝厚度的增加,焊后的残余应力逐渐减小,在厚度为 120μm时,焊后残余应力值最小,而后随着钎缝厚度的增加,应力值又逐渐增大,钎缝厚度存在最佳值;通过添加缓冲层,可以大大的缓解焊后的残余应力,且缓冲层的厚度存在最佳值。在能保证钎料对硬质合金表面润湿的前提下,钎料层越薄,对减少焊后残余应力越有利;在硬质合金上施加一定的压力,可以有效的降低焊后残余应力。在一定范围内增加压力,焊后残余应力减小;构件尺寸越大,钎焊面积越大,焊后的残余应力也越大。 采用美国AST公司生产的X—2001二维应力分析仪对硬质合金圆环两更多还原

【Abstract】 The cemented carbide has advantages of high hardness, resistant to elevated temperature, corrosion resistant and good wear-resistance. It has been widely applied in the hermetic unit, cutting-tools, die, measuring tools and anti-abrasive components and the effect is notable. But there will exist high residual stress and distortion, even cracks, near to the joint due to the mismatch of material performance during the cooling process of brazing with other materials. To large area cemented carbide cirque, it is easier to generate crack and dehiscence Therefore, it is significant to forecast the residual stress of the brazed workpiece between the cemented carbide and other materials.Nonlinear MARC software was used to analyze the magnitude and distribution of the residual stress and the sensitive area of the joint between the cemented carbide cirque and steel matrix by thermal-elastic-plastic finite element method. The influence of temperature on the material properties were taken into account. The residual stress near the joint was measured by micro-zone X-ray diffraction approach to test and verify the reliability of simulation.The simulation shows that: the effect of axial stress and circumferential stress on the strength of the brazed joint is very little, and radial stress is the main factor of joint damage. The residual stress in the contact surface between brazing seam and cemented carbide is the maximal, and the radial tensile stress reach to the maximum at the place of 0.4mm from the inner side of the cemented carbide, the axial tensile stress is the maximum in the inner side of the contact surface. The area near the inner side of the contact surface between cemented carbide cirque and brazing seam is the most serious damaging area.The effect of joint shape, the filler metal thickness, buffer layer, putting loadand the sizes of the component on the residual stress also were studied by simulation. When there is a notch on the steel matrix the residual stress is much higher than that of without notch on steel matrix due to notch restraint, so the notch is bad to the strength of the joint. The residual stress will decrease with the increase of filler metal thickness, when the thickness is 120 y m, the residual stress is the minimum, then the residual stress will increase with the increase of thickness. There exists an optimal value to the brazing seam;The residual stress will be released greatly by adding buffer layer, and the most suitable size of buffer layer exists. The thinner the thickness of the filler metal layer is, the less the residual stress is, so the filler metal should be thin under the condition of wettting the brazing surface; The residual stress will decrease effectively when put some load on the surface of the cemented carbide; The larger the sizes of component and the brazing area are, the higher the residual stress is.X-2001 two -dimensional stress analyzer was used to measure the surface stress of the steel matrix at the two sides of cemented carbide cirque and upper surface of cemented carbide cirque. The experimental data were compared with the finite element calculations. The finite element calculations were in good agreement with the general trend of the experimental data, and verified reliability of the simulation.更多还原