Formation of high hardness zirconia coatings by gas tunnel type plasma spraying

The high hardness zirconia (ZrO₂) coatings could be obtained at an atmospheric pressure by using a gas tunnel type plasma spraying. The characteristics of these high hardness ZrO₂ coatings were investigated. The Vickers hardness of the ZrO₂ coating at a short spraying distance was very high; a high hardness of more than H_v=1200 was achieved at the surface side of the coating. The microstructure of the obtained high hardness ZrO₂ coating was also investigated by the microscopic method. And the characteristics of the high hardness ZrO₂ coating was discussed in comparison with that of the coating formed by the conventional type plasma spraying. It was clarified that the ZrO₂ coating of the gas tunnel type was not only much harder but also less porous than that of the conventional type.     

离子渗ZrN与喷丸复合对TC4合金疲劳行为的影响

为改善钛合金耐磨和抗疲劳性能,采用离子渗技术在TC4钛合金表面先渗Zr,再渗N形成梯度ZrN合金化层,并与喷丸强化(SP)后处理复合。采用扫描电镜(SEM)、X射线衍射仪和显微硬度计分析测试了改性层的组织结构和硬度沿层深的分布,探讨了改性层对TC4钛合金疲劳性能的影响规律和作用机制。结果表明,TC4钛合金离子渗层由ZrN-TiN复合相表层和富氮的Zr-Ti固溶体次表层组成,表面以ZrN相为主,其硬度较基材提高了3.2倍,合理强度的喷丸后处理未造成渗ZrN层表面明显损伤,并使表层硬度进一步增大,硬度沿层深呈现梯度递减分布。渗ZrN层明显降低了TC4合金的疲劳抗力,此归于ZrN-TiN层韧性低、表面粗糙度大。SP后处理则使渗ZrN的TC4钛合金疲劳抗力显著提高,不仅远高于TC4钛合金基材,而且远大于SP处理状态,原因归于复合处理引入了数值高、分布深的残余压应力场,并使表面粗糙度降低、组织改善,有效抑制了疲劳裂纹的萌生和扩展。     

Mechanical property of Fe-base metallic glass coating formed by gas tunnel type plasma spraying

Metallic glass has excellent functions such as high toughness and corrosion resistance. Therefore it is one of the most attractive materials, and many researchers have conducted various developmental research works. However, the metallic glass material is expensive and a composite material is preferred for the industrial application. Thermal spraying method is one of potential candidates to produce metallic glass composites. The gas tunnel type plasma system, which has high energy density and efficiency, is useful for smart plasma processing to obtain high quality ceramic coatings such as alumina (Al₂O₃) and zirconia (ZrO₂) coatings. Also, the gas tunnel type plasma spraying can produce metallic glass coatings. In this study, the Fe-base metallic glass coatings were formed on the stainless-steel substrate by the gas tunnel type plasma spraying, and the microstructure and mechanical property were investigated. The Fe-base metallic glass coatings of about 200 μm in thickness were dense with a Vickers hardness of about Hv = 1100 at plasma current of 300 A. The abrasive wear resistance of Fe-base metallic glass coating was higher than the SUS substrate.     

Hardness, microstructure and surface characterization of laser gas nitrided commercially pure titanium using high power CO2 laser

Surface nitriding of commercially pure (CP) titanium was carried out using high power CO ₂ laser at pure nitrogen and dilute nitrogen (N ₂ + Ar) environment. The hardness, microstructure, and melt pool configuration of the laser melted titanium in helium and argon atmosphere was compared with laser melting at pure and dilute nitrogen environment. The hardness of the nitrided layer was of the order of 1000 to 1600 HV. The hardness of the laser melted titanium in the argon and helium atmosphere was 500 to 1000 HV. Using x-ray analysis the formation of TiN and Ti ₂ N phase was identified in the laser nitrided titanium. The presence of nitrogen in the nitrided zone was confirmed using secondary ion mass spectroscopy (SIMS) analysis. The microstructures revealed densely populated dendrites in the sample nitrided at 100% N ₂ environment and thinly populated dendrites in dilute environment. The crack intensity was large in the nitrided sample at pure nitrogen, and few cracks were observed in the 50% N ₂ + 50% Ar environment.     

Improvement of erosion resistance of titanium with different surface treatments

To improve the erosion resistance of titanium, several surface treatment methods were applied: (1) duplex treatment with carbon nitride film deposited on a plasma-nitrided layer, (2) diamond coating, and (3) laser alloying. Duplex treatment could improve the erosion resistance of titanium under a low impact velocity of erosion particles. However, under a high velocity of erosion particles, because of the shallow depth of the plasma-nitrided layer and low load-bearing capacity of carbon nitride layer on the plasma-nitrided specimen, the improvement of erosion resistance was not significant. Diamond coatings with a thickness of 15 μm made no significant improvement on the erosion resistance of the titanium substrate. The large-area spallation of diamond coating during erosion was observed, probably due to the high residual stresses, poor load-bearing capacity, and brittle nature of diamond coatings. Compared with untreated Ti substrate, the erosion resistance of the laser-alloyed (nitrided) specimen was improved significantly. The erosion mechanisms for laser-nitrided titanium were characterized by chipping, brittle fracture, and formation of large flakes in the laser-nitrided layers.     

Influence of gas flow rate on the microstructure and mechanical properties of hydroxyapatite coatings fabricated by gas tunnel type plasma spraying

Gas tunnel type plasma torch was used to spray hydroxyapatite (HA) coatings on 304 stainless steel substrate at different plasma gas (Ar) flow rates (100-170 l/min). Microstructure was observed by scanning electron microscope and phase analysis by X-ray diffraction. The mechanical properties such as hardness and abrasive wear resistance of HA coatings sprayed at different gas flow rates were investigated. The results showed that the gas flow rates affect greatly the microstructure and mechanical properties of HA coatings. Crystallinity increased and porosity decreased as the gas flow rate increased. Hardness and abrasion resistance increased as the gas flow rates increased.     

Bonding strength of DLC film on zirconia coating prepared by gas tunnel type plasma spraying

Bonding strength of diamond-like carbon (DLC) films on zirconia coatings prepared using a novel gas tunnel plasma spraying method has been studied and discussed. The emphasis is on the getting better characteristics of such doubly structured coatings (DSC) as comparing compared with properties of both components involved in the coatings. For the study of various failure mechanisms zirconia coatings of different thicknesses on aluminum substrates were prepared. The as-sprayed coatings were firstly polished and then subjected to deposition of DLC films. Adhesion of the DSC has been evaluated using a scratch test method. It has been found that the thicker coatings have higher hardness and lower porosity. The adhesion failures of DLC films on zirconia coatings (DSC) are caused by two different main mechanisms: (i) DLC films separation from the zirconia coatings, and (ii) DLC films breaking under stress load due to the brittleness of the material. In addition the adhesion failures are due to flaking of DLC films on the thinner zirconia coatings caused by a distortion of the aluminum alloy substrate coatings; and, chipping of DLC films themselves on the thicker zirconia coatings.     

钛型渣系气保护药芯焊丝焊接参数相互关系

采用高速摄影、平板实焊等试验方法,研究了钛型渣系气保护药芯焊丝焊接参数的技术特征、电弧形态、熔滴过渡形态以及焊接工艺参数间的匹配关系.结果表明,钛型渣系气保护药芯焊丝熔滴过渡的基本形态是非轴向排斥过渡,焊丝的电弧形态属于活动、连续型,焊丝熔滴过渡受主导力控制.该工艺方法的关键参数是焊接电流和电弧电压,它们之间存在最佳数...     

纳米PTFE粒子细化高速电喷镀镍基复合镀层的组织

利用高速电喷镀方法制备纳米聚四氟乙烯(PTFE)镍基复合镀层.采用X射线衍射(XRD)、电子探针、红外光谱等方法考察了纳米PTFE在复合镀层中的表现;应用扫描电子显微镜(SEM)、场发射环境扫描电子显微镜(FEGE-SEM)等技术探讨了纳米PTFE在镀层中的形态以及细化镀层组织的作用机理.结果表明,PTFE纳米粒子主要分布在镀层Ni晶粒的晶界面上而不是在晶粒内部,PTFE粒子粘附在固相Ni晶体上进而阻碍Ni原子的沉积使Ni复合镀层的晶粒细化.     

磨料粒径及形状对磨料水射流切割钛合金表面微观形貌的影响

采用不同粒径与形状的磨料颗粒,在磨料水射流切割平台上切割钛合金,用超景深显微镜等设备分析,以研究不同的磨料粒径及形状对钛合金表面微观形貌的影响。研究表明:磨料粒径越大,钛合金表面所形成的划痕越长,80目磨料颗粒形成的微划痕长度约为160目磨料的5倍。且球形磨料颗粒所形成的划痕末端堆积较少,其表面线粗糙度低于9.5 μm;具有棱边的磨料颗粒所形成的划痕有唇状或鳞片状金属堆积,其表面线粗糙度在9.5～13.0 μm间;柱体形的磨料颗粒冲击形成的划痕带有尖锐的棱角,其表面粗糙度大于13.0 μm。      

等离子束表面冶金原位颗粒增强铁基涂层的研究

采用等离子束表面冶金技术,在Fe、C合金粉末中添加强碳化物形成元素W、Cr和少量的Al,在低碳钢基体上制备出原位析出的颗粒增强铁基复合涂层.利用光学显微镜、扫描电镜和X射线衍射仪对冶金层显微组织和硬质颗粒的分布进行了观察、分析.结果表明：冶金层组织为过饱和的γ-Fe、原位析出形状良好细小弥散的复合碳化物（Fe,Cr,W,Nb）7C3和少量的AlFe,冶金层与基体呈冶金结合.在固溶强化、弥散强化和细晶体强化共同作用下,冶金层显微硬度可达到830HV0.1.     

Surface modification of polyester film by glow discharge tunnel at atmospheric pressure

A large-area improved dielectric barrier glow discharge tunnel has been developed for modifying the surface of polyester film at atmospheric pressure with argon and oxygen gas mixtures. The electrical properties of the glow discharge tunnel were studied by simultaneous measurement of the voltage and current. In addition, the effect of the glow discharge tunnel treatment on the surface of polyester film were studied. The resultant modifications of the surface properties of the treated samples were investigated through scanning probe microscopy and contact angle measurement.     

Surface modification of die casting mold steel by a composite technique of hot-dipping and plasma electrolytic oxidation

The hot dipping process of pure aluminum on H13 steel substrates followed by plasma electrolytic oxidation（PEO） was studied to form alumina ceramic coatings for protective purpose.H13 steel bars were first dipped in pure aluminum melts,and then,a reactive iron-aluminum intermetallic layer grew at the interface between the melt and the steel substrate.The reactive layer was mainly composed of intermetallic Fe-Al（Fe₂Al₅）;the thickness of aluminum layer and Fe-Al intermetallic layer were mainly influenced by dipping time（1.5～12.0 min） and dipping temperature（710～760 ℃）.After PEO process,uniform Al₂O₃ ceramic coatings were deposited on the surface of aluminized steel.The element distribution,phase composition and morphology of the aluminized layer,and the ceramic coatings were characterized by SEM/EDS and XRD.The distribution of hardness across the composite coating is demonstrated,and the maximum value reaches 1864 HV.The thermal shock resistance of the coated sample is also well improved.     

大面积等离子束表面冶金铁基涂层的成形机理及组织结构

采用等离子束表面冶金技术,通过多道搭接方式在低碳钢基体上制备大面积铁基复合超厚涂层。基于大面积涂层成形的特点,探讨搭接率与涂层厚度等的变化规律,并利用扫描电镜、X射线衍射仪、金相显微镜、显微硬度计及磨损试验分析测试了涂层的相组成、组织及性能。结果表明:表面冶金涂层厚度可达3.0 mm,无裂纹、气孔等缺陷;组织为γ-(Fe,Ni)枝晶、M23C6、CrB及原位合成的TiC陶瓷颗粒,与基体呈良好的冶金结合。由于颗粒强化、细晶强化和弥散强化等多种强化作用,大面积Fe基超厚涂层具有良好的耐磨性能。     

The characteristics of a low-power-consumption plasma jet and ceramic coatings

The effects of the composition of plasma gases (Ar-N₂, Ar-H₂), arc current, and voltage on the temperature and velocity of a low-power (5 kW) plasma torch in the arc field free region has been investigated using an enthalpy probe. Coatings of Al₂O₃-13TiO₂ were deposited under different conditions. The results show that in the Ar-N₂ plasma, the enthalpy, temperature, and velocity change little with arc current and voltage when regulating the nitrogen proportion in the plasma gas. The hardness of the resulting coatings is 800 to 900 kg/mm² HV.300. For Ar-H₂ plasma, however, increases in the H₂ content in the mixture of the gases remarkably enhanced the velocity and heat transfer ability of the plasma jet, with the result that the coatings showed high hardness up to 1200 HV.     

基于响应曲面法的Ar-N2等离子射流特性研究

目的 为了研究等离子射流特性,方法 本文借助响应曲面法,以粒子速度和温度作为指标来反映射流特性的变化,采用Box-Behnken-Design ( 简称BBD)设计分析了电流、主气以及次级气比例这三个影响因素对于射流特性的影响规律以及参数之间的相互作用关系。结果 研究表明：对于粒子速度的影响因素排序中：QAr > I > C, 对于粒子温度的影响因素排序中：I > QAr > C。该喷嘴下实现最佳加热效应的参数配比为：主气大小80L/min、电流450A,次级气比例为17.5%;实现射流最佳加速效应的离子气及电参数配比方案为：主气大小120L/min、电流450A,次级气比例为12.5%;在射流最佳加速效应对应参数下制备AT40涂层进行验证,发现涂层均匀致密,孔隙少。结论：运用响应曲面法分析和解决等离子射流特性影响问题具有科学性和可操作性,借助射流特性的研究能够有效指导涂层制备。     

Characteristics of high hardness alumina coatings formed by gas tunnel plasma spraying

High hardness alumina coatings were formed at atmospheric pressure by gas tunnel plasma spraying, and the characteristics of these coatings were investigated. The hardness on the cross section of the alumina coating at a short spraying distance was more than 1300 HV, and the thickness of the hard layer increased with an increase of power input. The microstructure of the alumina coating was investigated by microscopy and x-ray diffraction (XRD) methods. It was ascertained that the cell size was small (∼10 μn), and α-alumina was dominant in the high hardness layer of the coating. Finally, the effect of plasma energy was estimated from these results.     

纯钛表面Zr-N等离子合金化(英文)

为了改善纯钛的表面性能,利用等离子表面合金化技术在纯钛表面形成Zr-N改性层。对Zr-N改性层的微结构、成分及硬度进行测试,并对改性层形成及表面硬度提高的机理进行分析。利用球-盘磨损试验对表面改性纯钛的摩擦学性能进行研究。结果表明,在纯钛表面形成了均匀致密的Zr-N改性层,改性层由表面Zr-N化合物层和基体内Zr、N的扩散层构成。Zr-N表面改性层显著提高了纯钛的表面硬度,表层的最高硬度约为HK1040。Zr-N表面改性层没有减摩效果,但明显改善了纯钛的磨损性能。     

热等离子束照射工业纯钛快速渗氮制备表面氮化层

以热等离子束作为等离子源，以氮气、氢气混合气体作为工作气体，对工业纯钛进行表面渗氮处理，并利用显微硬度仪、X射线衍射仪、扫描电镜、金相显微镜分别对氮化后试样进行显微硬度测定、相结构及断面形貌分析。结果表明：在等离子束对试样进行15min的照射后即可在工业纯钛（TA2）表面获得具有一定厚度的硬度较高的氮化层。