Diffusion bonding SiC or Si3N4 to Nimonic 80A

A method of diffusion bonding SiC or Si₃N₄ to Nimonic 80A was developed to establish the fundamental technology for the application of ceramics to machinery components used at elevated temperature. An analysis of the thermal stress that occurs in ceramic/Nimonic 80A bonded composites was done using the finite element method, and a bonding experiment based on the analytical results was conducted. The composites were produced by the insert metal bonding method, using varying thickness of Ni, W, Kovar, Cu and so on. It was found that the residual thermal stress in the ceramic part of the composite was extremely low and that the composite had a tensile strength of more than 98 MPa at room temprature. Furthermore, the paper describes the feasibility of the application ofthis bonding method to components for marine diesel engines.     

Hot corrosion cracking of Nimonic 80A

Experimental investigations have been carried out to study the hot corrosion crack growth behaviour ofN imonic BOA in a combustion gas containing sulphur, vanadium or sodium at 600 and 700°C. The time to rupture has been found to be inversely proportional to the applied stress, and the crack growth rate, da/dt, can be described by the LEFMparameter K, the stress intensity factor. The threshold stress intensity factor, K_th , and the critical stress intensity factor, K_c, have been found to be functions oftemperature and corrodent level. In the case ofsulphur, K_th decreases continuously with increasing sulphur content in the fuel. In the case of vanadium or sodium, there appears to be a critical level ofcorrodent for the worst attack.     

Parametric Study of Temperature Distribution in Electrodischarge Diamond Grinding

Electrodischarge diamond grinding (EDDG) is a potential process for machining of advance engineering components, but there is no theory to support it. The work reported in this article makes an attempt in this direction. This article reports on determination of temperature distribution in the workpiece due to EDDG using the finite element method. The temperature distribution in the workpiece domain due to EDDG is obtained by superposition of the two temperature distributions for grinding and electrical discharge mechining (EDM) (i.e., 2D for grinding and axisymmetric for EDM). The effects of duty cycle, on-time, current, energy partition, time of machining, and feed velocity while machining are computationally investigated.     

铸态AZ80A 镁合金热加工图及高温变形行为研究

目的采用Instron5500R热模拟试验机,研究铸态AZ80A镁合金在变形温度为270~410℃、应变速率为0.001~0.5 s-1条件下的热加工图及高温变形行为。方法利用双曲正弦本构函数模型描述了铸态AZ80A镁合金的高温变形行为,计算获得了该合金的变形激活能,构建了应变量为0.3和0.6时的热加工图。结果得到了合金热变形本构模型及加工图,变形激活能为203.5k J/mol,确定了应变为0.3和0.6时的动态回复区域为与动态再结晶区域。结论铸态AZ80A镁合金在330~380℃,0.001~0.01 s-1时发生了动态结晶,这是该合金最佳的热加工工艺参数范围。     

终冷温度对(B+M/A)X80管线钢组织-性能的影响

通过HOP技术,使X80管线钢获取了(B+M/A)复相组织。采用力学性能测试、显微分析和X射线衍射方法研究了在不同终冷温度条件下(B+M/A)X80管线钢的组织演变规律,分析了显微组织对力学性能的影响。结果表明,随着终冷温度的升高,贝氏体的板条宽度增加,贝氏体的含量和位错密度减小以及残余奥氏体量增加,导致材料强度降低和塑性增加。在高的终冷温度条件下,马氏体的形成、碳化物的析出和残余奥氏体的分解是材料强度增加和塑性减小的内在因素。在不同终冷温度下,实验钢的屈强比都小于0.85,均匀伸长率大于0.8%,形变强化指数大于0.10,符合大变形管线钢的技术要求。     

配分温度对(B+M/A)X80大变形管线钢组织和性能的影响

采用热模拟方法,通过不同配分温度的HOP(Heating on-line partitioning)处理,使X80管线钢获得(B+M/A)复相组织和优良的变形能力。采用力学性能测试、材料显微分析和X射线衍射方法研究了在不同配分温度下(B+M/A)X80管线钢的组织演变规律,分析了显微组织对其力学性能的影响。研究结果表明,随着配分温度的升高,由于贝氏体板条宽化、位错密度降低、残余奥氏体含量增加和碳化物的粗化,导致实验钢的强度降低和塑性增加。当配分温度较高时,残余奥氏体稳定性和含量的降低是材料强度增加、塑性降低的显微组织因素。