摘要
本研究采用放电等离子烧结(SPS)方法在以Ni箔为中间过渡的304不锈钢基体上制备了Cu含量在10%~30%(质量分数)的TZM(钛-锆-钼)合金涂层。利用扫描电镜(SEM)与能谱(EDS)仪分析了合金涂层组织;通过维氏硬度仪和激光导热仪对合金涂层的硬度及热扩散系数进行了表征;采用热震循环试验对合金涂层的热震稳定性能进行了测试;综合以上分析结果研究了Cu含量对SPS烧结TZM合金涂层的组织及性能影响。结果表明:TZM合金涂层由白色的Mo相与灰黑色的Cu相组成;随着Cu含量的增加,TZM合金涂层的硬度和热扩散系数随之增加;热震循环试验结果表明,造成TZM合金涂层热震循环试验失效的主要原因是由于涂层各部分热膨胀系数不一致所产生的应力超过了涂层与过渡层界面处的结合强度,而Cl-在结合界面处的点蚀作用对合金涂层的开裂、脱落起到了促进作用;结合摩擦磨损试验后的磨痕形貌及EDS选区分析结果,合金涂层磨损机制为疲劳磨损和磨粒磨损,且摩擦磨损过程中发生了氧化行为。Cu含量的提高有效改善了合金涂层的摩擦磨损性能。
TZM(titanium-zirconium-molybdenum)alloy was a Mo-based alloy with Ti,Zr and C elements added with a mass fraction of no more than 1%,which had excellent properties and was widely used in the industrial field,mainly using powder metallurgy and smelting method to fabricate bulk alloy materials.However,the use of the above method to fabricate the block Mo-based alloy material as a whole increased the usage cost,and the use of alloy coating technology could effectively reduce the usage cost,but the Mo-based alloy coating fabricated by thermal spraying and other coating technologies often had problems such as low bonding strength between coatings and substrates,ununiform microstructure distribution and coating density was difficult to be controlled.The use of powder metallurgy methods could be used to fabricate Mo-based alloy coatings on high melting point substrates,but the popularization of such coating might be restricted undoubtedly due to the high cost of high melting point substrates.Therefore,the use of powder metallurgy methods to fabricate Mo-based alloy coatings on a low-cost substrate such as steel undoubtedly had potential application prospects.However,the melting point of steel and the like was much lower than that of molybdenum-based alloys,making it difficult to be used as a substrate material for powder metallurgy molybdenum-based alloy coatings.Since Mo-based alloy could also be fabricated on the surfaces of the parts that were subjected to wear and friction conditions,the coatings were required to have both anti-wear and anti-friction effects.For TZM alloys,the anti-wear effect could be achieved by carbides contained therein and the anti-frication could be achieved by molybdenum oxides generated during the wear process.Further improvement in anti-friction effect needed to be achieved by introducing other anti-friction phases.Considering the anti-friction lubrication effect of soft copper(Cu)and its low melting point characteristic than that of Mo-based alloys and steels,therefore,in the present work,low-cost Cu-modified TZM alloy coatings with Cu contents of 10%to 30%(mass fraction)were fabricate on 304 stainless steel substrates with nickel(Ni)foils as the intermediate transition layers by spark plasma sintering(SPS).The effects of Cu content on the microstructure characteristics,the distribution characteristics of chemical composition along the cross-section of the coating system,microhardness,thermal diffusivity,thermal shock stability and friction-wear property of the obtained coatings were studied using scanning electron microscope(SEM),energy dispersive X-ray spectroscopy(EDS),laser thermal conductivity tester,microhardness tester,friction and wear tester,and thermal vibration cycle test device.The results showed that the Cu-modified TZM alloy coatings achieved a tight bond with the 304 stainless steel substrates through the Ni transition layers,and there were no cracks between the transition layers and the coatings and the substrates.The alloy coatings were mainly composed of the Mo matrix phase and the Cu phase distributed between the Mo particles,and the two phases were in an incompatible mechanical mixing state.According to the distribution characteristics of the alloy elements along the coating cross-section,the coating system could be divided into five regions:stainless steel substrate region,Fe-Ni diffusion region,pure Ni region,Ni-Mo/Cu diffusion region and Mo/Cu alloy coating region.The thickness of the Fe-Ni diffusion region and the Ni-Mo/Cu diffusion region was about 15 and 10μm,respectively,indicating that a good metallurgical bond was obtained between the coating and the transition region,the transition region and the substrate,which was conducive to improving the bond strength.When the Cu content increased from 10%to 30%,the thermal diffusivity,microhardness and thermal shock cyclic cracking times of the Cu-modified TZM coatings increased gradually,while the friction coefficient decreased gradually.The average thermal diffusivity(room temperature~900℃),microhardness,and average thermal shock cyclic cracking times(600~1100℃)of the 30%Cu-modified TZM coating were respectively higher than those of the 20%Cu-modified TZM coating by about 81%,33%and 53%,and those of the 10%Cu modified TZM coating by about 155%,51%and 105%;and the average friction coefficient of 30%Cu-modified TZM coating was lower than that of 20%Cu-modified and that of 10%-modified TZM coatings by about 45%and 59%,respectively.The high thermal conductivity of Cu and its filling effect on the Mo matrix microstructure were the reasons that the thermal diffusivity,microhardness and average thermal shock cracking times of Cu-modified TZM alloy coatings increased with the increase of Cu content.The increasing lubricity of Cu and the oxide film generated during the friction and wear tests of the coatings was the reason that the friction coefficient decreased with the increase of Cu content.The internal stress produced due to the different thermal expansion coefficients between the Mo matrix phase,Cu filling phase,transition layer and 304 stainless steel substrate was the main reason for the coatings to crack and shed along the interface of the transition layers during the thermal shock cycles,and the pitting effect of the small amount of Cl^(-) remaining in the thermal shock cycling water had a promoting effect of the above-mentioned cracking and shedding.The wear mechanisms of the Cu-modified TZM alloy coatings were fatigue wear and abrasive wear.
作者
马玉康
侯清宇
马啸宇
光剑锋
唐木生
黄贞益
Ma Yukang;Hou Qingyu;Ma Xiaoyu;Guang Jianfeng;Tang Musheng;Huang Zhenyi(College of Metallurgical Engineering,Anhui University of Technology,Ma'anshan 243000,China;Anhui Magang Powder Metallurgy Co.,Ltd.,Ma'anshan 243000,China)
出处
《稀有金属》
EI
CAS
CSCD
北大核心
2022年第4期461-470,共10页
Chinese Journal of Rare Metals
基金
安徽高校自然科学研究项目(KJ2019ZD07)资助。
