Future developments in plasma spray coating

Abstract

Future coating developments for high–temperature gas turbine components is a topic which encompasses both material and process developments. The materials for use at high temperatures can be classified as wear (abradables and abrasives), corrosion, oxidation, and thermal barrier coatings. In spite of many interesting material modifications, the most important developments are associated with the application process, coating quality control procedures, and efficiency of operation regarding the source of material used to produce the coating.

MST/295     

Effect of plasma cutting on the fatigue and cracking resistance of steel

The results are presented of detailed examination of the effect of plasma cutting on the fatigue and cracking resistance of 14KhGNMDAFBRT steel.The thermal effect of the plasma arc increases the endurance limit of the hardened surface and heat-affected zone in comparison with the initial nonhardened material. The crack growth rate does not change.Translated from Problemy Prochnosti, No. 12, pp. 23–25, December, 1990.     

Effect of substrate surface roughening and cold spray coating on the fatigue life of AA2024 specimens

The effects of cold spray coating and substrate surface preparation on crack initiation under cyclic loading have been studied on Al2024 alloy specimens. Commercially pure (CP) aluminum feedstock powder has been deposited on Al2024-T351 samples using a cold-spray coating technique known as high velocity particle consolidation. Substrate specimens were prepared by surface grit blasting or shot peening prior to coating. The fatigue behavior of both coated and uncoated specimens was then tested under rotating bend conditions at two stress levels, 180 MPa and 210 MPa. Scanning electron microscopy was used to analyze failure surfaces and identify failure mechanisms. The results indicate that the fatigue strength was significantly improved on average, up to 50% at 180 MPa and up to 38% at 210 MPa, by the deposition of the cold-sprayed CP-Al coatings. Coated specimens first prepared by glass bead grit blasting experienced the largest average increase in fatigue life over bare specimens. The results display a strong dependency of the fatigue strength on the surface preparation and cold spray parameters.     

Effect of the thickness of plasma-sprayed coating on bond strength and thermal fatigue characteristics

NiCrAlY bond coat and ZrO2–8 wt% Y2O3 top coat with various thicknesses were deposited on Hastelloy X by plasma spraying. Residual stress was calculated by the finite element method (FEM) to explain the variations in the bond strength and thermal fatigue characteristics with the thickness of the bond coat and top coat. The bond strength of thermal barrier coatings (TBCs) increased with decreasing maximum residual stress in the y-direction of the top coat. The thermal fatigue characteristics increased with decrease of the maximum principal residual stress of the top coat and the thickness of oxidation layer of the bond coat.     

Effect of pulsed plasma nitriding on mechanical and tribological performance of Ck45 steel

We studied the mechanical properties and wear performance of AISI 1045 (Ck45) carbon steel under the influence of pulsed plasma nitriding. The treatments were performed at temperatures of 500 and 550 degrees C in N2:H2 gas ratios of 1:3 and 3:1 and the working pressure of 10 mbar for 1 to 4 hours. Samples were examined by X-ray diffraction, optical, electron and atomic force microscopy, microhardness tests, roughness measurements and wear tests. Nitride layers were mainly composed of epsilon-(Fe2-3N) or gamma'-(Fe4N) depending on the gas ratio and/or temperature and time. When the nitriding time is increased, the composition of the compound layer varies from monophase gamma'-(Fe4N) to the two phase of epsilon-(Fe2-3N) and gamma'-(Fe4N). The highest thickness and hardness of the layers were obtained at 550 degrees C in the N2:H2 gas ratios of 3:1 for 4 h. The topographical evolution and surface roughness of the samples showed that all the roughness parameters increase with increasing the temperature. The friction coefficient of all samples was higher than that of untreated material. Wear performance of all nitrided samples was significantly better than that of untreated material.     

NiCrBSi粉末火焰喷焊钢管的抗拉强度研究

采用氧乙炔火焰喷焊工艺在耐热钢管表面制备了镍基合金喷焊层,分别利用OM、SEM、EDS、TEM等方法分析了喷焊管表面与横截面的显微组织、形貌、元素分布及物相结构.通过拉伸实验测定了喷焊管的抗拉强度,观察了喷焊管的拉伸变形规律.结果表明,在实验工艺参数下,喷焊层内部形成了以γ-Ni固溶体为基体,呈弥散分布的富Cr针状第二相,以及硼硅酸盐玻璃相,在第二相粒子周围,γ-Ni固溶体内有大量位错缠绕.喷焊层与基体形成了冶金结合,整体抗拉强度高达522 MPa.拉伸后,钢管基体产生了延性裂纹,喷焊层发生了半脆性断裂.喷焊管同时具备了外层耐蚀耐磨性能与基材的良好韧性,综合性能有较大改善.