不同重熔处理对镍基粉末合金热喷涂件疲劳性能的影响

对以40Cr中碳合金钢为基体、镍基自熔性粉末合金为喷涂材料的热喷涂试样进行了4种不同时长的火焰重熔处理,进行了弯扭疲劳试验。应用扫描电子显微镜及能量衍射谱对不同试样的显微组织及成分进行了观察与分析,发现不同时长的重熔处理是影响热喷涂试样疲劳性能的关键因素。     

高频感应重熔Ni60AA合金粉末涂层的研究

针对某大型圆柱形工件,利用Ni60AA合金粉末,采用高频感应重熔工艺,在工件表面制备了合金涂层,并对涂层的组织进行了分析并测试了涂层的硬度和耐磨性。结果表明,感应熔涂制备的涂层与基体形成了良好的冶金结合,涂层与基体之间存在明显的＂白亮带＂,涂层基体中分布着丰富的硬质相,显著提高了涂层的硬度,具有良好的耐磨性。     

电接触强化对火焰喷涂Ni60-WC涂层及40Cr基材组织及性能的影响

在40Cr基材上利用氧-乙炔火焰喷涂镍基碳化钨(Ni60-WC)复合涂层后,对涂层进行电接触强化。通过金相显微镜观察电接触强化前后涂层截面的显微组织形貌,利用维氏显微硬度仪分析涂层截面的显微硬度分布,并通过SEM面扫描分析涂层与基材的钨元素分布。结果表明,电接触强化工艺能够显著提高涂层质量及硬度,并使涂层与基材间形成良好的冶金结合。     

热喷涂涂层封孔处理及其耐蚀性能研究

研制了一种主要针对钢铁企业镀锌生产线沉没辊和稳定辊热喷涂层的复合封孔剂,其具有良好的耐高温腐蚀性能和抗粘锌性能。采用刷涂方法,对热喷涂涂层进行封孔处理,并对封孔处理的涂层进行酸腐蚀、锌腐蚀和抗粘锌试验。研究结果表明,涂层中的孔隙基本已经被封孔剂所填充,降低了涂层的孔隙率。封孔涂层可以屏蔽或减缓外部腐蚀介质对涂层及基体的渗透作用,从而起到有效的防护作用。并且该复合封孔剂具有很好的抗粘锌性能。     

粉末的物理性能对热喷涂涂层的影响

在SUS316L不锈钢基体上,采用HVOF和DGS两种不同的工艺方法,分别喷涂WC-12Co和FeAl涂层,观察WC-12Co和FeAl粉末的颗粒形貌、粒度组成以及DTA,研究它们对热喷涂涂层质量的影响.通过表面粗糙度、显微硬度、形貌相以及X射线衍射谱等分析表明,球化程度高,颗粒大小均匀的粉末可使涂层的组织均匀,致密性好,结合强度高.采用HVOF方法喷涂WC-12Co涂层的质量最好,而采用DGS工艺喷涂FeAl涂层的工艺参数还有待于进一步优化.     

钛表面激光重熔Al/Ni组合涂层的组织及其抗氧化性能

利用等离子喷涂及电弧喷涂工艺在工业纯钛表面制备Al/Ni组合涂层,并对涂层进行激光重熔处理,使涂层之间、涂层与基体之间发生冶金反应,从而得到与基体有一定结合强度的NiAl金属间化合物涂层。研究了重熔前后涂层的微观组织及NiAl金属间化合物的形成机理,并对经重熔处理后的Al/Ni/Ti试件及纯钛试件进行了800℃/60 h高温氧化试验,讨论了涂层经高温氧化后的微观组织及其对钛材抗高温氧化性能的影响与防护机理。研究表明,Ni/Al涂层经激光重熔处理后,重熔反应区由多量的呈等轴晶状的Ni_2Al_3相以及少量的呈树枝晶状的NiAl相组成。重熔处理后的涂层经高温氧化后,Ni_2Al_3相的含量有所减少且结构疏松,而NiAl相则稳定存在并最终形成了具有一定厚度的区域。激光重熔处理后的Ni/Al组合涂层对Ti基体起到了较好的抗高温氧化作用。     

热处理对超音速火焰喷涂 NiCoCrAlY 涂层组织性能的影响

采用超音速火焰喷涂制备了NiCoCrAlY合金涂层,采用真空热处理工艺对涂层进行了后处理,研究了热处理前后涂层的结构形貌、界面以及涂层结合强度的变化。研究结果表明:热处理后涂层的缺陷和孔隙由8.3%降低至1.4%;SEM和EDS分析表明,涂层与基材之间发生了元素互扩散,涂层与基体形成了约20μm的扩散层,涂层的结合强度由42.1MPa提高到55.6MPa。热处理后,涂层/基体界面形成的扩散层改善了界面结合状态,有助于消除界面处的残余应力,并形成冶金结合,从而提高涂层的结合强度。     

热喷涂制备非晶合金涂层性能的研究进展

首先介绍了非晶合金的理论基础,然后从耐磨性和耐蚀性两个方面入手,详细地阐述了国内外对于热喷涂非晶合金涂层性能研究进展情况,并系统地总结了非金合金涂层在耐磨性和耐蚀性上的本质联系和根本矛盾,最后指出热喷涂非晶合金涂层性能研究上的局限性,提出三点问题:对于非晶合金基础理论的研究还处在起步阶段、热喷涂制备非晶合金涂层的合金体系种类少、制备非晶合金涂层的热喷涂技术有待开发,并针对以上三点问题提出热喷涂制备非晶合金涂层性能研究的未来发展方向。      

热喷涂WC-MoB-Co金属陶瓷涂层的耐腐蚀性能研究

本文采用团聚烧结法制备了WC-MoB-Co金属陶瓷喷涂粉末,使用超音速火焰喷涂技术在316L不锈钢基材上制备了WC-MoB-Co涂层;采用SEM、XRD表征了WC-MoB-Co粉末和腐蚀前后涂层的微观形貌及物相组成;测试了WC-MoB-Co涂层耐熔融锌铝腐蚀性能。研究结果表明,制备的WC-MoB-Co金属陶瓷复合粉末粒度集中、流动性好、松装密度高;WC-MoB-Co涂层结合强度高、孔隙率低;WC-MoB-Co涂层具有良好的耐腐蚀性能,随着腐蚀时间的延长,涂层中的WC颗粒逐渐参与反应。     

NiCr过渡层对高速火焰喷涂WC-Co涂层摩擦磨损性能及疲劳磨损性能的影响

WC-Co涂层作为一种性能优异的涂层,逐渐被应用于轧辊的表面防护,目前大量实验研究的有热喷涂、激光熔覆制备WC-Co涂层。本文提出用高速火焰喷涂(HVOF)在常用轧辊材料Q235钢表面制备WC-Co涂层,同时在WC-Co涂层和基体之间加入NiCr过渡层。利用SEM、XRD、摩擦磨损测试、疲劳磨损测试等测试方法,对涂层形貌结构以及各项性能与无过渡层涂层进行对比研究。结果表明,加入NiCr过渡层后,WC-12Co+NiCr、WC-10Co-4Cr+NiCr涂层硬度分别为1059.64 HV_0.3、1016.96 HV_0.3,比WC-12Co涂层(960.01 HV_0.3)、WC-10Co-4Cr涂层(1012.20 HV_0.3)更高。WC-12Co+NiCr涂层的磨损率(5.19×10^-15 m³·(N·m)^-1)远低于WC-12Co涂层(6.59×10^-15 m³·(N·m)^-1     

The chemical and mechanical processes of thermal fatigue degradation of an aluminide coating

The influence of strain history on the oxidation and mechanical degradation of an aluminide coating was examined by induction heating of stepped-disk specimens. The coating was applied to a single-crystal Ni-base superalloy (RENè N4) by pack aluminization. The anisotropic elasticity of the single-crystal substrate allowed simultaneously subjecting the aluminide coating to different strain amplitudes. Two distinct modes of coating degradation were observed for tests performed in air between temperature limits of 520 °C and 1080 °C: scalloping (spatially periodic surface oxidation and roughening) and cracking. The degree of scalloping became more severe as the compressive strain imposed on the coating was increased. Six thousand cycles between peak strains of -0.20 and 0.007 pct produced uniform surface oxidation, without scalloping, whereas 6000 cycles between peak strains of -0.56 and 0.01 pct gave oxidation and scalloping to 80 pct of the coating thickness. Cracks along coating grain boundaries were observed after 6000 cycles between peak strains of -0.45 and 0.16 pct. The depth of scalloping was found to correlate approximately with peak compressive substrate strain. Based on this correlation, a mechanism for scallop initiation and growth involving cyclic breakdown of the surface oxide and irreversible cyclic creep of the coating is proposed. Cracking along coating grain boundaries is attributed to tensile strains applied below the transition temperature of the coating. The results obtained from this study indicate that cyclic strain history is an important variable which should be included when determining the oxidation rate of coatings and alloys.     

The chemical and mechanical processes of thermal fatigue degradation of an aluminide coating

The influence of strain history on the oxidation and mechanical degradation of an aluminide coating was examined by induction heating of stepped-disk specimens. The coating was applied to a single-crystal Ni-base superalloy (RENè N4) by pack aluminization. The anisotropic elasticity of the single-crystal substrate allowed simultaneously subjecting the aluminide coating to different strain amplitudes. Two distinct modes of coating degradation were observed for tests performed in air between temperature limits of 520 °C and 1080 °C: scalloping (spatially periodic surface oxidation and roughening) and cracking. The degree of scalloping became more severe as the compressive strain imposed on the coating was increased. Six thousand cycles between peak strains of -0.20 and 0.007 pct produced uniform surface oxidation, without scalloping, whereas 6000 cycles between peak strains of -0.56 and 0.01 pct gave oxidation and scalloping to 80 pct of the coating thickness. Cracks along coating grain boundaries were observed after 6000 cycles between peak strains of -0.45 and 0.16 pct. The depth of scalloping was found to correlate approximately with peak compressive substrate strain. Based on this correlation, a mechanism for scallop initiation and growth involving cyclic breakdown of the surface oxide and irreversible cyclic creep of the coating is proposed. Cracking along coating grain boundaries is attributed to tensile strains applied below the transition temperature of the coating. The results obtained from this study indicate that cyclic strain history is an important variable which should be included when determining the oxidation rate of coatings and alloys.     

热喷涂Ag/Cu复合触头涂层组织及性能

分别采用等离子和高速电弧喷涂系统制备了Ag/Cu复合触头涂层,利用扫描电镜、划痕试验仪、显微硬度仪、双电桥法以及真空电弧烧蚀仪等分析测试了Ag/Cu复合触头涂层的组织及性能。结果表明:DH-X2等离子喷涂制备的Ag/Cu复合触头涂层孔隙、裂纹少,显微硬度范围89.7～106.1 HV,涂层与基体结合的临界载荷79.2 N,电导率68.5%IACS,截流值1.0A、燃弧时间2.6ms;而QD8高速电弧喷涂制备的涂层组织结构疏松,涂层内部有较大裂纹,并出现银氧化物相,显微硬度范围为58.3～74.6 HV,涂层与基体结合的临界载荷57.2 N,电导率53.7%IACS,截流值1.4A、燃弧时间2.7ms。DH-X2等离子喷涂制备Ag/Cu复合触头Ag涂层比QD8高速电弧喷涂制备的涂层组织及性能更加优异。     

感应重熔TiC增强Fe-Al金属间化合物复合涂层的显微组织研究

采用Fe粉、Al粉及TiC硬质颗粒等的混合粉料,利用火焰喷涂加感应重熔的方法得到TiC增强Fe-Al金属间化合物复合涂层,涂层中TiC颗粒含量为15%(质量分数)。用X射线衍射仪(XRD)测定复合涂层的物相组成。用扫描电子显微镜(SEM)观察复合涂层的微观形貌,涂层中出现了TiC增强Fe-Al金属间化合物区,TiC硬质颗粒在Fe-Al金属间化合物中呈白色点状分布。用维氏硬度计测得复合涂层的显微硬度为540.4MPa。     

连铸机拉矫辊等离子喷涂WC-20Cr-7Ni涂层性能

连铸机拉矫辊作为连铸机的重要组件,工作环境恶劣、磨损严重。为了降低连铸机拉矫辊工作过程中的辊面磨损,利用等离子喷涂技术在拉矫辊及H13钢板表面制备了厚度为0.2mm的WC-20Cr-7Ni涂层。通过水淬热冲击及轧制试验探究了WC-20Cr-7Ni涂层的抗热冲击性能及耐磨性,并对热冲击前后试样进行了金相分析及硬度测试。结果表明,WC-20Cr-7Ni涂层孔隙率较低,并具有较高的耐磨性及优异的抗热冲击性能,可以有效提升连铸机拉矫辊的使用寿命。     

The influence of a martensitic phase transformation on stress development in thermal barrier coating systems

Thermal barrier coatings (TBCs) provide thermal insulation and oxidation protection of Ni-base superalloys in elevated temperature turbine applications. Thermal barrier coating failure is caused by spallation, which is related to the development of internal stresses during thermal cycling. Recent microstructural observations have highlighted the occurrence of a martensitic bond coat transformation, and this finite-element analysis was conducted to clarify the influence of the martensite on the development of stresses and strains in the multilayered system during thermal cycling. Simulations incorporating the volume change associated with the transformation and experimentally measured coating properties indicate that out-of-plane top coat stresses are greatly influenced by the presence of the martensitic transformation, the temperature at which it occurs relative to the strength of the bond coat and attendant bond coat plasticity. Intermediate values of bond coat strength and transformation temperatures are shown to result in the highest top coat stresses. This article is based on a presentation in the symposium “Terence E. Mitchell Symposium on the Magic of Materials: Structures and Properties” from the TMS Annual Meeting in San Diego, CA in March 2003.     

The influence of growth rate and temperature on high cycle fatigue of Al−Al3Ni

High-cycle fatigue tests have been conducted on specimens of an Al?Al₃Ni eutectic alloy, unidirectionally solidified at selected rates from 1.39×10^?4 cm/s to 0.3 cm/s. Tests were conducted in air at 298, 458 and 683 K. Room temperature fatigue lives were independent of growth rate at low solidification rates (1.39×10^?4–8.33×10^?3 cm/s, but were markedly improved in samples grown at 0.3 cm/s. Materials grown at 8.33 × 10^?3 cm/s exhibited fatigue lives similar to those of the lower growth rates, despite gross misalignment due to cellular growth. At 0.5T _m (458 K) and 0.75T _m (683 K), the fatigue lives of the material grown at low solidification rates were dependent on growth rate. The dependence of fatigue life on growth rate at elevated temperatures appears to be due primarily to differences in cyclic creep rates as a result of varying interfiber spacings. Crack initiation and propagation mechanisms were established by metallographic and fractographic examination. Dislocation substructure-fiber interactions were studied by transmission electron microscopy.     

The influence of crack length on fatigue

The fatigue crack growth rateda/dN of short cracks and the transition to long crack behavior were investigated for ARMCO-iron. Deep notched specimens with very small notch radius (between 1.5 and 4 μm) were used. The experiments were performed with constant stress intensity ranges for various stress ratios; the fatigue crack growth rate was measured as a function of the crack length. The results permit a discussion of the mechanisms responsible for the different behavior of “short” and “long” cracks. Formerly Graduate Student, Institut für Formerly Graduate Student, Institut für