Effects of heat treatment on the corrosion resistance of carbon steel coated with LaMgAl11O19 thermal barrier coatings

LaMgAl11O19 thermal barrier coatings (TBCs) were applied to carbon steels with a NiCoCrAlY bond coat by plasma spraying. The effects of heat treatment on the corrosion resistance of carbon steel coated with LaMgAl11O19 TBCs were investigated in 3.5wt% NaCl solution using polarization curves, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray diffrac-tion (XRD). The results show that a large number of cracks are found in the LaMgAl11O19 TBCs after the samples are heat-treated, including some through-thickness cracks. The corrosion forms of the as-sprayed and heat-treated TBCs are uniform corrosion and pitting corrosion, respectively. The as-sprayed TBCs exhibit three EIS time constants after being immersed for less than 7 d, and then a new time constant ap-pears because of steel substrate corrosion. When the immersion time is increased to 56 d, a Warburg impedance (W) component appears in the EIS data. The EIS data for the heat-treated TBCs exhibit only two time constants after the samples are immersed for less than 14 d, and a new time constant appears when the immersion time is increased further. The heat treatment reduces the corrosion resistance of carbon steel coated with LaMgAl11O19 TBCs. The corrosion products are primarilyγ-FeOOH and Fe3O4.     

Quality evaluation for air plasma spray thermal barrier coatings with pulsed thermography

Pulsed thermography (PT) as a non-contact non-destructiv e evaluation (NDE) technique was employed to examine as-sprayed air plasma spray (APS) thermal barrier coatings (TBCs) for quality eval uation. Thickness and micro-structural characteristics play a vital ro le in determining the quality. In this pape r, PT logarithmic peak second-derivative m ethod was adopted to measure the thickness of top coat. Time dependent ther mal images were used to characterize the microstructure which was confirmed by scanning electron microscope (SEM). The results showed that there was relationship between the temperature distribution of the surface and microstructu re change in TBCs. Temperature distribution in thermal images and measurement results of thickness were in fairly good agreement with the microstructure change. It can be concluded th at it was possible to employ these NDE methods as quality evaluation for as-sprayed TBCs.     

GDC电极冷却水管喷涂工艺优化及评估

针对国际热核聚变实验堆(ITER)计划中直流辉光放电清洗(GDC)冷却水管的耐高压和热循环工况,在GDC水管上采用等离子喷涂技术制备了Al2O3陶瓷涂层,采用正交试验方法的极差分析和方差分析对等离子喷涂工艺进行了优化,得到了最佳工艺参数:电压60V、电流600A、喷涂距离100mm。在最佳工艺参数的条件下,对涂层进行了X射线衍射(XRD)分析和金相分析。结果表明,涂层表面99.9%以上的物相为Al2O3,涂层与基底结合紧密,测得涂层厚度为(324±11)μm,涂层整体厚度均匀。最后测试了涂层的耐电压能力,并对涂层进行了250次的室温至240℃热循环的试验,证明上述工艺可满足ITER苛刻工况的使用要求。     

Quality evaluation for air plasma spray thermal barrier coatings with pulsed thermography

Pulsed thermography(PT) as a non-contact non-destructive evaluation(NDE) technique was employed to examine as-sprayed air plasma spray(APS) thermal barrier coatings(TBCs) for quality evaluation.Thickness and micro-structural characteristics play a vital role in determining the quality.In this paper,PT logarithmic peak second-derivative method was adopted to measure the thickness of top coat.Time dependent thermal images were used to characterize the microstructure which was confirmed by scanning electron...     

镁合金表面反应热喷涂陶瓷涂层制备及性能

采用SHS反应火焰喷涂技术,把Al-CuO系铝热剂引入到喷涂材料中,在AZ91D表面成功制备了Al2O3基复相陶瓷涂层.试验结果表明,SHS反应热喷涂层抗热震性明显优于普通热喷涂层,热震次数可达40次左右,若辅以Ni-Al打底,喷后重熔工艺可使涂层热震到50次时仍完好无损;喷涂试样耐蚀性随着致密性的增大而提高,反应热喷涂层耐蚀性比基体提高36倍;Ni-Al打底,喷后重熔后可提高至基体的160倍:清漆封孔后几乎不发生腐蚀,耐蚀性最好.     

Microstructural evolution and growth kinetics of thermally grown oxides in plasma sprayed thermal barrier coatings

The formation of thermally grown oxide(TGO) during high temperature is a key factor to the degradation of thermal barrier coatings(TBCs)applied on hot section components. In the present study both the Co Ni Cr Al Y bond coat and Zr O_2-8 wt.% Y_2O_3(8YSZ) ceramic coat of TBCs were prepared by air plasma spraying(APS). The composition and microstructure of TGO in TBCs were investigated using scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and X-ray diffraction(XRD) analysis. The growth rate of TGO for TBC and pure BC were gained after isothermal oxidation at 1100 °C for various times. The results showed that as-sprayed bond coat consisted of β and γ/γ'phases,β phase reducesd as the oxidation time increased. The TGO comprised α-Al_2O_3 formed in the first 2 h. Co O, Ni O, Cr_2O_3 and spinel oxides appeared after 20 h of oxidation. Contents of Co O and Ni O reduced while that of Cr_2O_3 and spinel oxides increased in the later oxidation stage.The TGO eventually consisted of a sub-Al2O3 layer with columnar microstructure and the upper porous CS clusters. The TGO growth kinetics for two kinds of samples followed parabolic laws, with oxidation rate constant of 0.344 μm/h~(0.5) for TBCs and 0.354 μm/h0.5for pure BCs.     

等离子喷涂钼基非晶纳米晶复合涂层的组织和电化学特性

用Mo基合金粉末(含Si,B,Cr,W,Mo,Ni等)作为喷涂材料,利用大气等离子喷涂(APS)技术,在0Cr13Ni5Mo不锈钢基体上制备了钼基非晶纳米晶复合涂层.利用XRD观察了涂层的晶型结构,扫描电镜(SEM)观察涂层的组织形貌,恒电位扫描仪对涂层的电化学特性进行了测试,显微硬度仪测量涂层的显微硬度.实验结果表明,利用等离子喷涂工艺可以制备高硬度的Mo基非晶纳米晶复合涂层,这种涂层结构均匀致密,其显微硬度最高达到1 426.9HV.孔隙率约为5.5%.非晶纳米晶复合涂层在3.5%NaCl溶液中存在钝化现象,自腐蚀电流为6.459μA·cm-2,腐蚀速度0.869 mm·a-1.     

两种镍基合金喷焊层的相分布与热疲劳性能

利用扫描电子显微镜、X射线衍射仪及透射电子显微镜观察分析了含Cu和Mo(Ni-A)、不含Cu和Mo(Ni-B)两种镍基合金喷焊层样品的组织、相分布和成分分布,分别测定了基体部位、热影响区、结合区及涂层内的显微硬度. 利用高频加热炉对两种喷焊层进行了热疲劳实验,对经热疲劳实验后喷焊层微观组织进行了观察,分析了喷焊层内的相分布和成分分布状态,探讨了热疲劳裂纹产生和扩展的过程及规律. 结果表明:两种喷焊层内均有针状富Cr第二相弥散分布,具有较好的热疲劳性能. Ni-A样品喷焊层可以分成两个区域:在靠近基体的区域均匀地分布着块状富Cr第二相;在离表层200μm左右的区域内分布有针状富Cr第二相,体积比块状富Cr第二相小几十倍. Ni-B样品喷焊层内只有针状富Cr第二相,在整个喷焊层内均匀分布. Ni-A样品喷焊层由于过渡区域的存在,具有比Ni-B样品喷焊层更好的热疲劳性能. 热疲劳实验前后样品的EDS分析结果表明两种喷焊层内的各相有较好的热稳定性.     

高温固相法制备Sm2O3掺杂La2Ce2O7热障涂层材料

以La2 O3、CeO2和Sm2 O3为原料,采用高温固相反应法制备了Sm2 O3部分掺杂La2 Ce2 O7热障涂层陶瓷材料,其化学式为(SmxLa1-x)2Ce2O7.采用X射线衍射法研究了试样的物相结构,并通过对比各实验条件下制备的试样的X射线衍射图谱,对试样的掺杂比例、烧制温度及烧制时间进行了探究.结果表明,所制备试样为萤石结构,当掺杂摩尔比Sm：La为1：2或1：3时试样均能保持良好的相结构,以掺杂摩尔比Sm：La=1：2制备的( Sm0.33 La0.67)2 Ce2 O7材料在1600℃下具有良好的相稳定性,且其最佳制备条件为1550℃下烧制10 h,该材料是一种很有潜力的新型热障涂层陶瓷材料.     

Microstructure and high-temperature wear properties of in situ TiC composite coatings by plasma transferred arc surface alloying on gray cast iron

In this work, an in situ synthesized TiC-reinforced metal matrix composite (MMC) coating of approximately 350–400μm thick-ness was fabricated on a gray cast iron (GCI) substrate by plasma transferred arc (PTA) surface alloying of Ti–Fe alloy powder. Microhard-ness tests showed that the surface hardness increased approximately four-fold after the alloying treatment. The microstructure of the MMC coating was mainly composed of residual austenite, acicular martensite, and eutectic ledeburite. Scanning electron microscopy (SEM) and X-ray diffraction analyzes revealed that the in situ TiC particles, which were formed by direct reaction of Ti with carbon originally contained in the GCI, was uniformly distributed at the boundary of residual austenite in the alloying zone. Pin-on-disc high-temperature wear tests were performed on samples both with and without the MMC coating at room temperature and at elevated temperatures (473 K and 623 K), and the wear behavior and mechanism were investigated. The results showed that, after the PTA alloying treatment, the wear resistance of the sam-ples improved significantly. On the basis of our analysis of the composite coatings by optical microscopy, SEM with energy-dispersive X-ray spectroscopy, and microhardness measurements, we attributed this improvement of wear resistance to the transformation of the microstruc-ture and to the presence of TiC particles.     

Microstructure and mechanical properties of titanium nitride coatings for cemented carbide cutting tools by pulsed high energy density plasma

Hard, wear-resistant and well-adhesive titanium nitride coatings on cemented carbide cutting tools were prepared by the pulsed high energy density plasma technique at ambient temperature. The results of Auger spectra analysis indicated that the interface between the coating and substrate was more than 250 nm. Under optimized deposition conditions, the highest critical load measured by nanoscratch tester was more than 90 mN, which meant that the TiN film was well adhesive to the substrate; the highest nanohardness and Young抯 modulus according to nanoindentation tests were near to 27 and 450 GPa. The results of cutting tests evaluated by turning hardened CrWMn steel in industrial conditions indicated that the wear resistance and edge life of the cemented carbide tools were enhanced dramatically because of the deposition of titanium nitride coatings. These improvements were attributed to the three combined effects: the deposition and ion implantation of the pulsed plasma and the becoming finer of the grain sizes.     

等离子喷焊Mo-Fe-Cr-B合金覆层的组织性能研究

采用等离子喷焊法在Q235钢表面熔敷一层Mo-Fe-Cr-B合金覆层,借助光学显微镜、SEM、EDS、XRD、显微硬度计及电化学工作站等对该覆层的组织结构及性能进行表征分析。结果表明,Mo-Fe-Cr-B合金覆层组织由均匀分布的α-Fe、Mo_2FeB_2、(Mo,Cr,Fe)_3B_2和(Cr,Fe)7C3等相组成;覆层与Q235钢基体形成良好的冶金结合,在熔合线附近存在元素的相互扩散;覆层显微硬度最高可达871HV0.3,其为Q235钢基体硬度的4倍;覆层耐腐蚀性能强于Q235钢及Ni60覆层。