Wear Properties of Plasma Transferred Arc Fe-based Coatings Reinforced by Spherical WC Particles

Fe-based coatings reinforced by spherical WC particles were produced on the 304 stainless steel by plasma transferred arc(PTA) to enhance the surface wear properties. Three different Fe/WC composite powder mixtures containing 0 wt%, 30 wt%, and 60 wt% of WC were investigated. The microstructure and phase composition of the Fe/WC composite PTA coatings were evaluated systemically by using scanning electron microscope(SEM) and X-ray diffraction(XRD). The wear properties of the three fabricated PTA coatings were investigated on a BRUKER UMT TriboLab. The morphologies of the worn tracks and wear debris were characterized by using SEM and 3 D non-contract profiler. The experimental results reveal that the microhardness on the cross-section and the wear resistance of the fabricated coatings increase dramatically with the increasing adding WC contents. The coating containing 60 wt% of WC possesses excellent wear resistance validated by the lower coefficients of friction(COF), narrower and shallower wear tracks and smaller wear rate. In the pure Fe-based coating, the main wear mechanism is the combination of adhesion and oxidative wear. Adhesive and two-body abrasive wear are predominated in the coating containing 30 wt% of WC, whereas threebody abrasion wear mechanism is predominated in the coating containing 60 wt% of WC.

STUDY ON PTA CLAD (Cr,Fe)_7C_3/γ-Fe CERAMAL COMPOSITE COATING

A wear resistant （Cr, Fe）7C3/γ-Fe ceramalcomposite coating wasfabricatedon substrate of a 0.45% C carbon steel by plasma transferred arc （PTA） cladding process using the Fe-Cr-C elemental powder blends. The microstructure, microhardness and dry sliding wear resistance of the coating were evaluated. Results indicate that the plasma transferred arc clad ceramal composite coating has a rapidly solidified microstructure consisting of blocky primary （Cr, Fe）7C3 and the interblocky （ Cr, Fe）7C3/γ-Fe eutectics and is metallurgically bonded to the 0.45%C carbon steel substrate. The ceramal composite coating has high hardness and excellent wear resistance under dry sliding wear test condition.

Effects of Y_2O_3 on the microstructure and wear resistance of cobalt-based alloy coatings deposited by plasma transferred arc process

Cobalt-based alloys with different Y2O3 contents were deposited on Q235A-carbon steel using plasma transferred arc （PTA） welding machine. The effect of Y2O3 on the microstructure and wear resistance properties of the cobait-based alloys were investigated using an optical microscope, a scanning electron microscope （SEM）, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. It was found that a cobalt-based solid solution with a face-centered cubic crystal structure was presented accompanied by the secondary phase M7C3 with a hexagonal crystal structure in the Y2O3-free cobalt-based alloy coating. Several stacking faults exist in the cobalt-based solid solution. The addition of Y2O3 leads to the existence of the Y2O3 phase in the Y2O3-modified coatings. Though stacking fault exists in the Y2O3-modified coatings, its density increases. The addition of Y2O3 can refine the microstructure and can increase the wear resistance properties when its contents are less than or equal to 0.8 wt.%. However, further increase of its contents will lead to the agglomeration of undissolved Y2O3 particles at the γ-Co grain boundary, and will lead to a coarse microstructure and lower wear resistance properties.

Influences of the microstructure on the wear resistance of cobalt-based alloy coatings obtained by plasma transferred arc process

The microstructure, substructure, and wear characteristic of cobalt-basedalloy coatings obtained by plasma transferred arc (PTA) process were investigated using opticalmetallurgical microscope, X-ray diffraction (XRD), scanning electron microscope (SEM), transmissionelectron microscope (TEM), and dry sand abrasion tester (DSAT). The aging effect on the structureand wear resistance of the cobalt-based PTA coating was also studied. The results show that theas-welded coating consists of cobalt-based solid solution with face-centered cubic structure andhexagonal (Cr,Fe)_7C_3. There are a lot of stacking faults existing in the cobalt-based solidsolution. After aging at 600 deg C for 60 h, the microstructure becomes coarse, and another carbide(Cr,Fe)_(23)C_6 precipitates. As a result, the wear mass loss of the aged sample is higher than thatof the as-welded sample.

Corrosion Behavior of Plasma Transferred Arc Fe-based Coating Reinforced by Spherical Tungsten Carbide in Hydrochloric Acid Solutions

Fe-based coatings reinforced by spherical tungsten carbide were deposited on 304 stainless steel using plasma transferred arc(PTA) technology.The composition and phase microstructure of the coatings were evaluated using scanning electron microscopy(SEM),energy dispersive spectrometer(EDS) and X-ray diffraction(XRD).The corrosion behaviors of the coatings in 0.5 mol/L HCl solution were studied using polarization curve and electrochemical impedance spectroscopy(EIS) measurements.The experimental results shows that the tungsten carbide improves the corrosion resistance of the Fe-based alloy coating,but increase in the mass fraction of tungsten carbide leads to increasing amount of defects of holes and cracks,which results in an adverse effect on the corrosion resistance.The defects are mainly present on the tungsten carbide but also extend to the Fe-based matrix.The tungsten carbide,acting as a cathode,and binding material of Fe-based alloy,acting as an anode,create a galvanic corrosion cell.The binding material is preferentially corroded and causes the degradation of the coating.

Ni/Al Intermetallics Plasma Transferred Arc Processing

In-situ alloy development during surface processing allows for a limitless materials selection to protect components exposed to severe service conditions. In fact surface alloying offers the possibility to strengthen surface components with alloys that would not be possible to process otherwise. This work used Plasma transferred arc (PTA) hardfacing for surface alloying. Different amounts of aluminium powder, 5-25%, were added to a Ni based superalloy, from Hastealloy C family, in the atomized form. The mixture was homogeneized in a ball mill and PTA deposited on carbon steel substrate. The influence of different processing parameters on the final surface alloy was evaluated as current intensity and depositing velocity were varied. Coatings were characterized by optical and scanning electronic microscopy, X-ray diffraction and Vickers microhardness profiles, under a 500g load. Results showed that PTA hardfacing is an adequate surface alloying. For the conditions tested increasing hardness was obtained by solid solution for the lower amounts of Al added and due to the new intermetallic phases for the richer Al mixture.

Cr_3C_2／镍基合金等离子堆焊层的组织及耐磨性能

采用光学显微镜、扫描电镜、X射线衍射仪以及磨损试验机等,研究了加入不同量的Cr3C2对等离子堆焊镍基合金堆焊层组织和耐磨性能的影响。结果表明:纯镍基合金堆焊层组织主要是由γ(Ni,Fe)、CrB和M7(C,B)3等物相构成,且存在着明显的成分偏析;加入Cr3C2以后,合金层中出现了Cr3C2相,且使堆焊层枝晶破碎,组织变细,成分偏析减弱直至消失;Cr3C2颗粒的加入,提高了堆焊层的磨粒磨损性能,且随其加入量的增加,耐磨性逐渐提高;当加入量达到30％时,耐磨性最好,随后耐磨性开始降低。

钼对等离子堆焊钴基合金组织结构及性能的影响

采用光学显微镜,扫描电镜(SEM),X射线衍射(XRD),透射电镜(TEM)和磨粒磨损试验,研究了8%Mo对等离子堆焊钴基合金组织结构和性能的影响。结果表明,堆焊合金层主要是由面心立方的γ(Co)和六方结构的M7C3构成,并且在钴基固溶体中存在着许多堆垛层错。8%Mo的加入,没有改变合金层的相结构,但其亚结构却发生了变化,堆垛层错消失,在钴基固溶体中出现了大量的位错。8%Mo的加入,不但可以细化钴基固溶体和共晶体组织,还可以提高合金层中富Cr碳化物相的相对含量,有助于提高合金层的硬度和耐磨性能。

WFLC-11钴基合金激光熔覆层组织及性能评价

对自主开发的WFLC-11激光熔覆专用钴基合金粉末激光熔覆层与Stellite-6合金等离子喷焊层的组织与性能进行了比较研究。结果表明,激光熔覆层组织细小、均匀,致密性好,高温硬度更高,其显微硬度、耐腐蚀性能、抗擦伤性能优于Sellite-6合金等离子喷焊层。

固溶时效对等离子堆焊WCp/18Ni300钢复合涂层组织与性能的影响

采用等离子堆焊技术在Cr5钢表面制备WC增强18Ni300钢复合涂层.研究添加质量分数为25%和35%的球形WC对堆焊层组织与性能的影响,分析固溶(900℃×1 h)和时效(490℃×5 h)处理前后堆焊层的显微组织/相变过程/显微硬度和摩擦磨损性能.结果表明,在马氏体时效钢粉末中添加WC颗粒影响堆焊层组织和马氏体相变.WC/MS300复合堆焊涂层的显微组织主要以奥氏体为主.经固溶时效热处理后,基体试样硬度和摩擦磨损性能下降,而WC/MS300试样中γ-F转变为α-Fe,硬度和耐磨性显著改善,添加35%WC试样耐磨性能最佳.由WC的微观结构演变表明,固溶时效后WC颗粒周围形成厚的扩散层,显著改善了界面结合.

钴基合金等离子转移弧喷焊组织结构和性能研究

应用光学金相、扫描电镜 (SEM )、X射线衍射 (XRD)、透射电镜 (TEM )和显微硬度测试对钴基合金等离子喷焊的组织结构和显微硬度 ,以及时效过程中的物相和显微硬度变化进行了研究。结果表明 ,合金层主要是由γ(Co)和 (Cr ,Fe) 7(C ,B) 3构成。表现出亚共晶的组织形态。它在时效过程中物相发生了变化 ,并且发生了由 (Cr ,Fe) 7(C ,B) 3向Cr2 3(C ,B) 6 的转变过程 ,时效后显微硬度平均提高约 11%。研究表明 ,时效过程中新相的析出。

等离子弧堆焊原位合成TiB2基涂层及其抗高温氧化性能研究

利用等离子弧堆焊设备,通过钛粉与碳化硼粉末之间的冶金反应,在普通碳钢表面制备了TiB2基金属陶瓷层。分析了焊接工艺对熔覆层组织及缺陷的影响,确定了稀释率对原位合成TiB2的影响,并从冶金角度分析了缺陷的形成原因。研究了TiB2熔覆层的高温抗氧化性,试验结果表明以63Ti37B4C为配方可得到抗氧化性更加优良的TiB2的金属陶瓷层。

球形WC增强铁基复合等离子堆焊层的组织与摩擦学性能

为提高304不锈钢的摩擦学性能,将质量分数为30%和60%的球形WC添加到铁基复合粉末,采用等离子堆焊技术在其表面制备了WC增强铁基复合涂层.分析其显微组织结构、物相和显微硬度,在恒定载荷(50 N)和滑动速度(20 mm/s)下进行干摩擦磨损试验,研究其干滑动摩擦学性能.结果表明:富含Cr的固溶强化奥氏体、高硬度的Cr7C3和WC增强相的存在,提高了WC增强铁基堆焊层的硬度,30%WC和60%WC涂层的显微硬度达到HV0.2665和HV0.2724,比铁基涂层提高了21.1%和31.9%,是304基体的3.7和4倍;30%WC和60%WC涂层的摩擦系数和磨损率分别为0.59和2.639×10^(–6) mm^3·N^(–1)·m^(–1),0.42和1.111×10^(–6) mm^3·N^(–1)·m^(–1).30%WC和60%WC涂层均表现出优异的耐磨性能,其磨损机理分别为黏着磨损和二体磨粒磨损的混合机制,和三体磨粒磨损.

枪体工作高度对等离子束表面合金化熔池成形的影响

以球墨铸铁表面的等离子束合金化过程为主要研究对象,熔池的宽度、深度、熔化效率和熔池形貌为成形特征参数,研究了等离子枪工作高度变化对熔池成形的影响。从热输入的角度研究了工作高度的变化对等离子束合金化熔池成形产生影响的机理。结果表明:随工作高度的增加,熔池的宽度、深度和熔化效率都先上升后下降,即这三种特征参数都存在一个最佳的工作高度值。随着工作高度上升到一定高度,熔池的表面逐渐变得粗糙,熔池轨迹边缘的清晰度和直线度也变差。工作高度的变化并不能对熔池成形造成直接影响,但其可以间接影响熔池的实际热输入功率和功率密度分布,进而导致熔池宽度、深度、熔化效率和表面形貌发生变化。

等离子喷焊在汽轮机阀芯零部件司太立合金堆焊中的应用

汽轮机阀门类零件常需要在内孔(如燃机套筒)或外圆(如高压进汽管、抽汽管、阀杆等)面堆焊司太立合金以达到高温耐磨的要求,本文叙述等离子喷焊技术成功应用于此类零件司太立合金的堆焊,并介绍从设备、工艺、试验到生产各方面的研究过程。

Tandem rapid manufacturing of Inconel-625 using laser assisted and plasma transferred arc depositions

This paper presents an investigation on depo- sition of Inconel-625 using laser rapid manufacturing （LRM） and plasma transferred arc （PTA） deposition in individual and tandem mode. LRM has advantages in terms of dimensional accuracy, improved mechanical properties, finer process control, reduced heat input and lower thermal distortion, while PTA scores more in terms of lower initial investment, lower running cost and higher deposition rate. To quantify the clubbed advantages and limitations of both processes, these were studied individually and in tandem. A number of samples were deposited at different process parameters like power, scan speed, powder feed rate. They were subjected to tensile test, adhesion-cohesion test, impact test and micro hardness measurement. The results of individual tests showed the comparable mechanical prop- erties with i20% variation. The mixed dendritic-cellular and dendritic-columnar microstructures were respectively observed for LRM and PTA deposits with a distinct inter- face for the case of tandem deposition. The interface strength of tandem deposits was evaluated employing adhesion-cohesion test, and it was found to be （325 i 35） MPa. The study confirmed the viability of LRM and PTA deposition in tandem for hybrid manufacturing.

Plasma transferred arc forming technology for remanufacture

The plasma transferred arc （PTA） forming remanufacturing technology was introduced in this paper. This technology includes plasma surfacing, deposition and rapid forming technology. With self-developed plasma forming system, the thrust of engine cylinder body was remanufactured by PTA powder surfacing. In the concrete, the Nil5 alloy was deposited on the thrust face of the body in order to recover its dimension. In addition, the reman- ufacturing forming with Fe-based, Inconel 625 alloy was studied. The microstructure and hardness of the as-depos- ited materials were investigated.

等离子熔覆CoCrCuFeNiMn高熵合金组织研究

采用等离子熔覆技术在Q235钢基体上制备了fcc结构的Co Cr Cu Fe Ni Mn高熵合金熔覆层,并研究了熔覆层的组织结构以及合金元素在基体中的扩散。结果发现,熔覆层显微组织为树枝晶,枝晶间为富Cu面心立方固溶体,晶格常数为0.3597 nm,有纳米编织组织析出。枝晶内为多种元素固溶的面心立方固溶体,晶格常数为0.3664 nm。高熵组元元素在熔合线靠近热影响区一侧形成元素的过渡区,过渡区宽度约为10μm。临近熔合线的热影响区内出现了大约70μm宽的铁素体带,该区域的珠光体因脱碳分解生成铁素体,Co在该区域扩散的距离最远。

灰铸铁表面原位合成TiC复合强化层的摩擦磨损性能

通过等离子束表面合金化工艺用Ti-Fe合金粉末在灰铸铁表面制备了原位合成Ti C复合强化层。结果表明,合金化层厚度为350~400μm,与基体之间实现良好的冶金结合,合金化后试样表层硬度最高可达969 HV0.2,合金化区显微组织为残留奥氏体、针状马氏体和共晶莱氏体。XRD及SEM分析观察发现,在合金化区存在原位复合Ti C颗粒。通过销-盘型高温摩擦磨损试验对合金化试样和未经合金化处理的灰铸铁试样的室温及高温（473 K、673 K）下的摩擦磨损行为及机理进行了对比研究,磨损试验结果表明,合金化处理后,试样的耐磨性能相对于灰铸铁基体得到了明显改善,磨损率普遍下降3个数量级。根据扫描电镜（SEM）观察、能谱（EDS）检测和显微硬度测试分析结果可知,基体表层组织转变和Ti C颗粒是Ti C复合强化层耐磨性能提高的主要原因。

Effect of Different Surface Treatment Methods on the Friction and Wear Behavior of AISI 4140 Steel

In this study,the effects of various surface treatments on the friction and wear behavior of AISI 4140 steel have been evaluated.Sample surfaces of AISI 4140 steel were treated by quenching,carburizing,boronizing and plasma transferred arc （PTA） modification.The microstructural characteristics of surface treated steel samples were examined by optical microscopy and scanning electron microscopy （SEM）.The mechanical properties of the samples including the surface roughness,microhardness,and abrasive and adhesive wear characteristics were also evaluated.Wear tests were applied by using a block-on-disc configuration under dry sliding conditions.The wear behavior and friction characteristics of the samples were determined as a function of sliding distance.Each sample group was compared with the other sample groups,and it was observed that the carburized samples demonstrated the lowest weight losses;however,PTA-treated samples demonstrated the lowest coefficient of friction in comparison to the other sample groups at the same sliding distance.