Surface hardening of Fe-based alloy powders by Nd:YAG laser cladding followed by electrospark deposition with WC-Co cemented carbide

This paper presents the results of a study concerned with the surface hardening of Fe-based alloys and WC-8Co cemented carbide by inte- grating laser cladding and the electrospark deposition processes. Specimens of low carbon steel were processed firstly by laser cladding with Fe-based alloy powders and then by electrospark deposition with WC-SCo cemented carbide. It is shown that, for these two treatments, the electrospark coating possesses finer microstructure than the laser coating, and the thickness and surface hardness of the electrospark coating can be substantially increased.

Interface behavior study of WC92-Co8 coating produced by electrospark deposition

ESD (electrospark deposition) is a promising process to produce hard and wear-resisting coatings on metallic substrates. In this paper microstructure and interfacial characteristics of the WC92-Co8 coated on titanium and carbon steel are presented. A metallurgical bonding between the coating and substrate is obtained. The Ti element was found to distribute in WC92-Co8 at the metal pool, as well as the interface by diffusion. Some new phases were produced in the coating layer due to the chemical reaction during the ESD process. Experimental observation and thermodynamic analysis were utilized to study the mechanism of ESD.

Research on depositing Ni45 alloy on titanium alloy surface by electrospark deposition

Taking Ni45 bar as electrode,a strengthened layer of thickness up to 50μm was built up on BT20 titanium alloy matrix by means of electrospark deposition.Results of phase analysis by using of X-ray diffraction confirmed that the deposition layer was composed mostly of three phases,NiTi,NiTi2 and Ti.The surface microhardness of the deposition layer was up to 910 HV0.05,about 2.7 times as high as that of the matrix.The hardness at the cross-section of the entire deposition layer showed a gradient distribution.The effects of capacitance and deposition time on thickness of deposition layer were also studied,and results showed that with relatively low capacity and short deposition time the deposition layer without cracks can be obtained.

Characterization and wear behavior of WC-0.8Co coating on cast steel rolls by electro-spark deposition

To prepare high wear resistance and high hardness coatings, electro-spark deposition was adopted for depositing an electrode of a mixture of 92wt%WC＋8wt%Co on a cast steel roll substrate. The coating was characterized by classical X-ray diffractometer （XRD） and scanning electron microscopy （SEM） with energy dispersive X-ray analysis （EDX）. The results indicate that the coating shows nanosized particulate structure and dendritic structure including columnar structure and equiaxed structure. The primary phases of the coating contain Fe3W3C, Co3W3C, Fe2C and Si2W. The coating has a low friction coefficient of 0.13, its average wear-resistance is 3.3 times that of the cast steel roll substrate and the main mechanism is abrasive wear. The maximum microhardness value of the coating is about 1573.9 Hv0.3. The study reveals that the electro-spark deposition process has the characteristic of better coating quality and the coating has higher wear resistance and hardness.

Mechanism of Building-Up Deposited Layer during Electro-Spark Deposition

This paper studies the mechanism of formation of the deposit layer by (ESD) electro-spark deposition process. Inconel 738 substrates are coated with a deposited layer of NI6625 (Inconel 625). Selections of these two alloys have been done because they had wide applications and importance in the industry especially in gas turban blades in inland stations and in aircraft engines. ESD is suggested because it has a low input heat process which eliminates the effect of HAZ in these Ni-superfluous due to their sustainability to micro-cracks. The coating contains many deposited sub-layers coming from evaporated and melted micro-regions as a result of locally high heat generated by discharging a series of capacitors charged and discharged in a controlled manner between electrode and substrate material. The maximum deposition rates at the beginning of the process and decreases until been in a steady state condition due to the nature of the resultant morphology of the created surface.

Influence of Carbon Content of WC-Co Electrode Materials on the Wear Resistance of Electrospark Coatings

In the electrospark deposition (ESD) of WC-Co materials on low carbon steel, tungsten carbide (WC) decarburization is observed. The use of an inert atmosphere (argon) does not eliminate the problem of tungsten carbide decarburization during electrospark processing. The effect of the carbon concentration of electrode materials on the phase composition and mechanical properties of WC (10 wt% of Co) ESD coatings has been investigated in this work. The introduction of additional carbon (graphite) in the electrode material on the basis of the WC-10%Co leads to an increased amount of WC in the obtained coatings and thus improves their wear resistance.

Electrospark Coatings Based on WC-Co Alloys with Aluminium Oxide and Carbon Additives

The structure and properties of coatings based on WC-Co alloys containing additives of 1% - 5% aluminium oxide and 2.5% - 4.5% carbon were investigated. The coatings had a nanocrystalline structure. Depending on the duration and frequency of the discharge pulses, the ratio between WC and W2C in the coatings was different. The additives in the hard alloy allowed us increase the microhardness and wear resistance of the coatings by a factor of 2 - 3 in comparison to coatings created using a conventional WC-10%Co alloy.

钢表面电火花沉积合成W-Mo高熔点复合涂层

目的 采用ZY-10型电火花堆焊/涂层沉积设备,分别以钼和钨棒料为电极,以超纯氩气为保护气体,在PCrNi3MoVA钢基体表面沉积合成W-Mo高熔点复合涂层。方法 在PCrNi3MoVA钢基体表面先沉积出一定厚度的钼涂层作为打底层,在此基础上,采用更高的电参数沉积硬度和熔点都较高的钨涂层。作为同族元素的钼和钨,在高温电弧作用下能较好地合成W-Mo高熔点复合涂层。通过对复合涂层的成分、微观形貌等进行观察和分析,用等离子烧蚀实验检测复合涂层的抗烧蚀性能,并计算复合涂层的质量烧蚀率和线烧蚀率。结果 采用电火花沉积工艺在PCrNi3MoVA钢基体表面成功制备了W-Mo高熔点复合涂层,其厚度达到100μm以上,该复合涂层主要由W、Mo、Fe等成分组成,且越靠近涂层表面,W和Mo元素的含量越高,复合涂层主要有Mo、MoC、Fe_(2)Mo_(3)、Fe_(2)W等物相,复合涂层的耐烧蚀性能较好,在前10 s内其线烧蚀率仅为0.090~0.267 mm/s。结论 W-Mo高熔点复合涂层的厚度随着沉积次数和沉积电压的增加而增加;复合涂层与基体相互熔融,具有较好的冶金结合特征;复合涂层能够承受等离子火焰的短时高温冲击与冲刷,增加复合涂层的厚度可以有效抑制涂层试样烧蚀率的增加。

M CrAlY/TaC Metal Matrix Composite Coatings Produced by Electrospark Deposition

MCrAlY/TaC metal matrix composite coatings with 10, 20 and 30 wt.% TaC have been successfully produced by electrospark deposition （ESD）. The effects of TaC content on microstructure, hardness and oxidation behavior of the composite coatings were studied. The results showed that the composite coatings were composed of superfine 9＇ columnar dendrite and large TaC particles dispersedly distributed. The hardness was enhanced but oxidation resistance of the composite coatings was reduced with increasing TaC contents.

Preparation and mechanical properties of two nickel base alloy coatings achieved by electrospark deposition

Ni398 and Ni818 base alloy coatings were deposited on 1045 steel by electrospark deposition technique （ESD）. Forming properties, thickness, microhardness and wear resistance of the coatings were investigated. The chemical composition and cross- section morphology were analyzed through energy dispersive spectrum （EDS） and metalloscope. The results show that the technological parameter window of Ni398 is larger than that of Ni818 electrode. However, other properties of the Ni818 coating, such as thickness and microhardness, were better than those of the Ni398 coating. Especially the wornout volume of Ni818 coating is only 1/6 of that for 1045 steel and 1/3 for Ni398 coating. Chemical composition analysis indicated that the addition of Mo promoted grain refinement of nickel alloy. Metallographic analysis shows that the molten droplets of Ni398 coatings have an average structure thickness of 20-40 #m while the microstructure of Ni818 coatings is flat with width of 5-20 #m.

Q235钢表面电火花沉积铁基非晶改性层及其性能

采用电火花沉积技术在Q235钢表面制备了Fe基改性层,以提高Q235钢的硬度、耐磨性和抗高温氧化性。通过X射线衍射(XRD)、扫描电镜(SEM)、能谱仪(EDS)和高温循环氧化试验对比了基体和改性层的微观结构及抗高温氧化性能。结果表明,所得改性层为非晶态结构,在700℃退火6 h能实现晶化转变;改性层厚度约为12.5μm,表面呈现丘陵状形貌,与基体之间存在很好的冶金结合;电极成分中的Al、Cu和Sn分布于改性层整个表面,并且在凸起和凹陷处的含量更高;相对于基体,改性层具有更好的抗高温氧化性能。改性层的显微硬度为265.90 HV,高于基体和晶化转变改性层,耐磨性也更优。

电火花沉积工艺参数对涂层质量影响的研究现状

电火花沉积作为一种比较成熟的表面处理技术,输入热量小,对基材的热冲击和变形小,涂层与基材为冶金结合,广泛应用于零件表面改性和失效零件表面的修复。本文介绍了电火花沉积技术的原理,总结了近年来国内外电火花沉积技术的主要工艺参数(脉冲能量、比沉积时间、电极尺寸、沉积接触力和沉积气氛)对涂层质量、沉积效率、涂层硬度、厚度的影响规律。近年来,电火花沉积技术与其他技术相结合,可进一步提高涂层质量,通过双电极沉积方式的运用和设计,可得到复合涂层和复相涂层,扩大涂层应用范围。

转向架关键部件低热输入增材修复工艺研究

为优选转向架金属部件局部增材修复用的补焊工艺,文章将电火花沉积、火焰钎焊和脉冲冷焊3种低热输入焊接工艺用于40Cr钢的局部焊补,通过微观组织观察、硬度分布测试、弯曲和剪切性能测试评估补焊层的结合强度,并通过焊后工件的变形量和热影响区拉伸性能评判补焊工艺对工件的整体影响程度。结果表明:电火花沉积工艺的连接强度难以满足转向架部件的使用要求,不适用于转向架部件的局部缺陷修复;火焰钎焊以黄铜焊丝作为钎料时,连接界面存在脆性的Fe-Si界面反应层,致使连接强度降低。此外,火焰钎焊虽然加热温度低,但加热时间长,形成较宽的热影响区,不仅试件变形较大,而且热影响区的抗拉强度比母材下降20%,也不适用于转向架关键部件进行局部增材修复。脉冲冷焊工艺具有结合强度高、热影响区窄、对母材性能影响小及焊后工件变形小等优点,并且所需焊材方便生产现场就地取材,工艺过程简单,是3种备选工艺中最适合于对转向架关键金属部件进行局部增材修复的工艺方法。

BT20钛合金电火花沉积TiC涂层的微观组织研究

以石墨为电极,采用电火花沉积的方法在BT20钛合金表面制备TiC强化涂层。通过XRD、SEM、EDS和EPMA等检测手段对涂层的微观组织进行研究。结果表明:TiC强化层是反应涂层,强化相TiC由电极元素C和基体元素Ti反应生成。涂层的厚度不均匀,但涂层与基体实现了冶金结合。

工艺参数对TC11钛合金表面电火花沉积TiN涂层显微组织和磨损性能的影响（英文）

系统研究了工艺参数(放电电压x,氮气流量l和比强化时间s)对电火花沉积TiN涂层显微组织和耐磨性能的影响规律。以涂层厚度(TOC)、TiN含量(CON)和孔隙率(POC)来表征涂层显微组织。建立了一个数学模型来确定对涂层显微组织和耐磨性能影响最显著的参数。结果表明:放电电压x和氮气流量l对大多数指标都有较大影响,比如涂层厚度、摩擦因数(COF)和磨损失重(I_d),而比强化时间s对孔隙率影响较大,对其他指标影响不显著。试验得到最佳工艺参数为:放电电压60 V,氮气流量15 L/min和比强化时间3 min/cm^2。由于涂层磨损机制的变化,涂层磨损失重随放电电压和氮气流量的变化而变化。在最佳工艺参数下,TiN涂层的主要磨损机理为微观切削磨损伴随轻微断裂磨损。

H13钢表面电火花沉积钼涂层的摩擦磨损特性研究

在H13钢表面电火花沉积钼合金涂层,研究了其组织结构及摩擦磨损特性。结果表明,钼合金涂层由白亮层、扩散层和热影响区组成;钼元素与基体元素相互扩散形成冶金结合;合金层的显微硬度(约为1482HK0.025)较H13钢(280HK0.025)提高5倍左右;电火花沉积Mo合金层后摩擦系数明显降低,磨损质量损失仅为基材的1/7,抗磨性能显著提高。

钛合金表面电火花沉积WC涂层的研究

以WC为电极 ,采用不同的电火花强化工艺 ,在钛合金表面制备了强化涂层。为了比较不同工艺条件下获得涂层的组织结构 ,确定最佳的电火花沉积工艺 ,通过金相、SEM、EDS等试验方法对涂层的微观组织结构进行了研究。结果表明 ,仅改变电火花沉积参数对获得性能优良的沉积涂层效果不明显 ,当复合超声加工 ,并且达到一定频率范围时 ,可以明显改善涂层质量。所获涂层是由基体中Ti元素与WC电极发生反应生成的反应涂层 ,涂层的主要成分是TiC、W和W2 C。

电火花沉积MCrAlY涂层及其高温氧化行为

采用DZ-1600型电火花沉积设备在不锈钢表面电火花沉积MCrAlY涂层,研究了工艺参数对沉积效率的影响以及涂层的组织结构和抗氧化性能之间的关系。结果表明,沉积效率与输出功率成正比,频率对沉积效率几乎无影响。涂层表面呈"泼溅状"形貌,整体呈现纳米级微晶堆垛结构,反映了沉积过程的快速冷凝机制。XRD分析结果显示,高温氧化后在涂层表面形成的氧化膜主要由Al2O3组成。在1000℃空气中氧化200h的结果表明,获得的MCrAlY涂层具有优异的抗高温氧化与抗剥落性能。

高Al、Ti含量镍基高温合金激光、微弧火花表面熔焊处理研究进展及解决熔焊裂纹的途径

Al、Ti是镍基高温合金主要沉淀强化元素,随着Al、Ti含量的增加,镍基高温合金γ′-Ni3(Al,Ti)相体积百分数增加,高温强度增加,但是热裂纹敏感性也随之增加,如何利用熔焊工艺实现高Al、Ti镍基高温合金材料的表面无损伤熔焊处理一直是高Al、Ti镍基高温合金叶片与热端部件制造与再制造面临的难题。文中从高温合金表面熔焊修复与强化问题出发,着重介绍了高温合金焊接冶金问题及焊接性改善途径、激光与微弧火花两种低热输入熔焊工艺在高温合金表面修复与强化领域的研究与应用进展。分析表明:高Al、Ti镍基高温合金表面熔焊处理的主要难题是其高的热裂纹敏感性,主要表现在焊接或焊后热处理过程中容易产生凝固裂纹、液化裂纹、应变时效裂纹,采用惰性气体保护、改变基体组织状态、使用低强度的合金焊料、降低热输入等措施可有效改善其焊接性;激光、微弧火花等低热输入焊接工艺在解决高Al、Ti镍基高温合金表面熔焊问题方面具有极大的潜力。

TC1合金表面电火花沉积WC-8Co涂层界面行为

钛合金在航空、航天工业得到了广泛应用。但其耐磨性差,对磨面容易产生粘结及对微动磨损敏感等缺点,限制其应用领域的进一步扩大。实践证明,采用电火花强化技术在TC1合金表面制造WC-8Co强化层,可以有效提高TC1基体表面耐磨性能。作者研究了WC-8Co强化层的表面状态、界面行为以及相结构组成,认为TC1合金表面强化高熔点的WC-8Co材料,厚度可大于50μm;强化层与基体之间存在过渡区;强化层表面由TiC、W_2C和少量W组成;强化层截面的显微硬度是基体的3倍以上。