Laser surface alloying of medium carbon steel with SiC(P)

Laser surface alloying (LSA) is increasingly recognised as a powerful surface modification tool to enhance the wear and corrosion resistance of engineering components. The present work deals with laser alloying of medium carbon steel with silicon carbide using a high-power CO₂ laser. A processing regime, identifying an appropriate laser power-scan speed combination for achieving defect-free alloyed layers, has been established during the study. The influence of repetitive scans on the alloyed layer properties was also subsequently investigated in a comprehensive manner. Repetitive scanning was found to affect substantially the laser-alloyed zone (LAZ) and heat-affected zone dimensions, as well as the phase constitution of the laser-alloyed layers. The microstructure in the LSA layers was also observed to vary significantly with the number of scans, besides changing quite distinctly with depth in the LAZ. Tribological tests revealed considerable improvement in abrasive wear performance by laser surface alloying, and the results also emphasise the need to control the number of repetitive scans to achieve optimum performance.     

Laser surface alloying of case hardening steel with tungsten carbide and carbon

Abstract

The laser surface alloying process was used to introduce two different alloying materials, tungsten carbide (WC/Co) and carbon, into the molten surface of a case hardening steel (16MnCrS5), to improve its hardness and wear resistance. The chemical composition and the resulting microstructure in the alloyed layers were of particular interest in this investigation, because the strengthening mechanism was strongly dependent upon the type and amount of the alloy material. For laser alloying with carbon the increase in hardness and wear resistance was based on the martensitic transformation in the composition range concerned. For alloying with tungsten carbide it was necessary to consider two different strengthening mechanisms, namely, martensitic transformation and precipitation of carbides. In both cases the grain refinement in the laser affected zone had an additional effect. Resistance to dry abrasive sliding wear was measured using a conventional pin-on-disc wear testing machine. For both alloy materials the wear rate was substantially lower than that of a substrate that had been laser remelted without alloying additions.

MST/1556     

Microstructure and wear resistance enhancement of cast steel rolls by laser surface alloying NiCr–Cr3C2

The laser surface alloying technique was used to form wear resistant layers on 70MnV cast steel rolls with NiCr–Cr₃C₂ powders. The objective was to investigate the effects of the scanning speed on microstructure, phases, microhardness and wear resistance. Results indicate that the alloyed layers had dense, pore and crack free and homogeneous structures, as well as a metallurgical bonding with the substrates. With the increase of scanning speed, volume of retained austenite in the alloyed layer increased, microhardness and wear resistance increased and the microstructure refined. Wear results indicated that the wear resistance of the alloyed layer was enhanced by 7.8 times compared with that of the cast steel substrate. The improvement in wear resistance was attributed to the combined results of the grain refining effect, the solution strengthening effect, the tough γ-Fe matrix of the layer, the distribution of the hard Cr₇C₃, Fe₃C and martensite phases, and the good bonding between these hard phases and the matrix.     

Laser surface coating of Mo–WC metal matrix composite on Ti6Al4V alloy

Laser surface alloying of Mo, WC and Mo–WC powders on the surface of Ti6Al4V alloys using a 2 kW Nd-YAG laser was performed. The dilution effect upon the microstructure, microhardness and wear resistance of the surface metal matrix composite (MMC) coating was investigated. With a constant thickness of pre-placed powder, the dilution levels of the alloyed layers were found to increase with the incident laser power. The fabricated surface MMC layer was metallurgically bonded to the Ti6Al4V substrate. The microhardness of the fabricated surface layer was found to be inversely proportional to the dilution level. The EDAX and XRD spectra results show that new intermetallic compounds and alloy phases were formed in the MMC layer. With the existence of Mo content in the pre-placed powder, the β-phase of Ti in the MMC coating can be retained at the quenching process. With increasing weight percentage content of WC particles in the Mo–WC pre-pasted powder, the microhardness and sliding wear resistance of the laser surface coating were increased by 87% and 150 times, respectively, as compared with the Ti6Al4V alloy. The surface friction of the laser-fabricated MMC coatings was also decreased as compared with the worn Ti6Al4V substrate.     

激光重熔对NiCrBSi等离子喷涂层显微结构和性能的影响

1Crl8Ni9Ti不锈钢表面的NiCrBSi等离子喷涂层存在孔洞及与基体结合差等缺陷,为此进行了激光重熔处理.采用扫描电镜和显微硬度压痕仪分别对涂层的显微结构和力学性能进行了对比研究,采用SRV试验机评价了涂层激光重熔前后的滑动摩擦磨损性能,研究了激光重熔对NiCrBSi等离子喷涂层结构和性能的影响.结果表明:经过激...     

Microstructure and Properties of Laser Surface Alloying 304 Stainless Steel with Si

Silicon was added to the surface of 304 stain-less steel by laser melting the sprayed preplaced Sipowders.The optical microscopy,X-ray diffractionand EPMA were employed to investigate themicrostructure and chemical composition of thelaser surface alloyed layer.The hardness of the al-loyed layer was measured by microhardness testand wear resistance was evaluated by scratch test.Corrosion resistance of laser alloyed sample wasstudied in 1N H_2SO_4+0.1N NaCl and0.5N HCl+0.5N NaCl aqueous solutions.Amicrocrystalline intermetallic compound coatingwith smooth surface and good chemicalhomogeneity without porosity and crack is ob-tained.The hardness is about 720 HV.The wear re-sistance is 2 times better than that of the substrate.The corrosion resistance of the laser alloyed sampleis much better than that of 304 stainless steelsample.     

铜合金表面热喷涂镍基合金层激光重熔后的显微组织及耐磨性能

为了满足工业领域铜合金传热、耐磨、耐腐蚀性能优异的要求,对铜合金表面先等离子喷涂NiCrFeWBC自熔合金层,再进行激光重熔.采用现代分析技术研究了重熔处理对涂层显微组织及耐磨性能的影响.结果表明:等离子喷涂NiCrFeWBC自熔合金涂层重熔后层状组织、孔洞等缺陷完全消失,激光熔覆层与铜基体为冶金结合,涂层致密、组织均匀;熔覆层由表及里依次呈等轴晶、树枝晶及胞状晶形貌,并有WC,W_2C,Ni_3B等颗粒析出;熔覆层磨损性能明显高于铜合金基体及热喷涂涂层,磨损机理为典型的磨粒磨损.     

氩弧重熔对20G钢渗硼层组织结构和耐磨性能的影响

为了降低渗硼层的脆性,提高其耐磨性,对20G钢渗硼层进行了氩弧重熔处理,研究了渗硼层重熔前后的形貌、相结构、显微硬度及耐磨性。结果表明：渗硼层由FeB和Fe2B两相组成,经氩弧重熔处理后FeB相消除,氩弧重熔渗硼层由Fe23（C,B）6和Fe2B相组成,包括氩弧重熔区和过渡区;氩弧重熔处理使渗硼层表层微观硬度降低,且使...     

Laser Modification of Plasma Sprayed Alumina Coating

An alumina coating was developed on mildcarbon steel by plasma spraying and then modifiedby laser remelting.Some characteristics of plasmasprayed ceramic coating before and after laserremelting,such as microstructure,wear resistance,heat shock resistance,hot corrosion property andbond strength,have been investigated in this paper.     

In situ formation of TiC particulate composite layer on cast iron by laser alloying of thermal sprayed titanium coating

Commercial flake graphite cast iron substrate was coated with titanium powder by low pressure plasma spraying and was irradiated with a CO₂ laser to produce the wear resistant composite layer. The macro and microstructural changes of an alloyed layer with the traveling speeds of laser beam, the precipitate morphology of TiC particulate and the hardness profile of the alloyed layer was examined. From the results, it was possible to composite TiC particulate on the surface layer by direct reaction between carbon existed in the cast iron matrix and titanium with thermal sprayed coating by remelting and alloying them using laser irradiation. The cooling rate of the laser remelted cast iron substrate without a titanium coating was about 1 × 10⁴ K/s to 1 × 10⁵ K/s in the order under the condition of this study. The microstructure of the alloyed layer consisted of three zones; the TiC particulate precipitate zone (MHV 400–500), the mixed zone of TiC particulate + ledeburite (MHV 650–900) and the ledeburite zone (MHV 500–700). TiC particulates were precipitated as a typical dendritic morphology. The secondary TiC dendrite arms were grown to a polygonized shape and were necking. Then the separated arms became cubic crystal of TiC at the slowly solidified zone. In the rapidly solidified zone near the fusion boundary, however the fine granular TiC particulates were grouped like grapes.     

Improving the wear resistance of M41 steel by nitrogen alloying and ESR

AISI M41 high-speed steel (HSS) is considered as a super-hard tool steel due to high hardness level (65–70 HRC). Nitrogen alloying of AISI M41 HSS produces marked solid solution hardening and precipitation strengthening in addition to an improvement in pitting resistance. The mechanical properties in general, and wear resistance in particular, are strongly affected by the steel cleanliness and the status of non-metallic inclusions in steel. For this reason tool steel should be subjected to a secondary refining process. In this work, the wear characteristics of AISI M41 HSS were investigated. The effect of nitrogen alloying and electroslag refining (ESR) of this steel grade were considered. Both conventional and nitrogen alloyed grades were melted in open air induction furnaces and then remelted under three different compositions of calcium fluoride-based flux in an ESR machine. The wear behaviour of the resulting steels, for both conventional and nitrogen-alloyed grades before and after ESR, was monitored. The addition of nitrogen improves markedly the wear resistance of AISI M41 HSS. This improvement depends on the total nitrogen content and is independent on the form of the nitrogen constituent. The ESR process improves markedly the wear resistance of both conventional and nitrogen-alloyed grades.     

Enhancement of wear resistance of ductile iron surface alloyed by stellite 6

This paper deals with the improvement of the wear resistance of ductile iron surface alloyed by a hypoeutectic stellite 6 alloy. In this regard, the surface alloyed layer with 3 mm thickness deposited on ductile iron using tungsten inert gas (TIG) surface processing. The microstructure, hardness and wear resistance of surface alloyed layer were investigated using optical microscopy, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis, Vickers hardness (HV0.3) and pin-on-plate tests. The results showed that the microstructure of the surface alloyed layer consisted of carbides dispersed in a Co-based solid solution matrix with dendritic structure. This microstructure was responsible for the improvement of the hardness and wear resistance of the coating. Further investigations showed that the dominant mechanism of the wear in the coated and uncoated samples was delamination wear.     

Improved surface properties of D2 steel by laser surface alloying

The wear and the high-temperature oxidation resistance of the D2 steel (Fe-1.5 C-12 Cr-0.95 Mo-0.9 V-0.3 Mn) were increased by laser surface alloying after coating the surface with SiC or Cr₃C₂ powder. The surface alloys exhibit two microstructures: hypoeutectic and hypereutectic, respectively, all containing iron solid solutions and iron-chromium carbides, (Fe,Cr)₇C₃. The oxidation resistance of these alloys was measured in isothermal and cyclic conditions, and was shown to increase with silicon or chromium additions, particularly due to the formation of a chromia scale with excellent behaviour during thermal shoks. The surface alloy obtained with Cr₃C₂ also has shown a better resistance to wear due to its hypereutectic microstructure.     

SiC含量对激光熔覆SiC/Ni60A复合涂层显微组织和耐磨性能的影响

利用LDM2500-60半导体激光器在45#钢板上制备SiC颗粒增强Ni60A合金激光熔覆涂层,系统研究SiC含量对涂层的显微组织、稀释率、耐磨性、摩擦因数和显微硬度的作用规律。结果表明:随着SiC含量增加,熔覆表层的微观组织细化,稀释率、耐磨性、摩擦因数和硬度均先增加后降低;当SiC含量为20%(质量分数,下同)时,熔覆层的耐磨性能最佳,磨损量仅为0.0012g,为基体磨损量的1/36.3;摩擦因数最小为0.464,且磨损过程最为平稳;熔覆层平均硬度值最高,达到1039.9HV0.2,为基体的3.5倍;但当SiC含量达到25%时,熔覆层的显微硬度与耐磨性能反而下降。     

Laser surface remelting of Cu–Cr–Fe contact material

Abstract

Laser surface remelting/resolidifying treatment on a powder metallurgically manufactured Cu–Cr–Fe contact material was studied. Test results showed that a compact remelting/resolidifying layer was obtained with appropriate laser treatment conditions and a suitable surface absorption coating. After such treatment, the Cu–Cr–Fe microstructure was greatly refined and the Cr phase was uniformly dispersed in the Cu rich matrix with fine spherical or near spherical form. Improved compactness and microstructure of the laser remelted Cu–Cr–Fe material yielded increased hardness (by ~80%), wear resistance, and a reduced friction coefficient compared with the base material. The mechanism of laser strengthening is discussed in relation to the microstructural features of the Cu–Cr–Fe material.     

TiAl合金表面激光重熔等离子喷涂MCrAlY涂层研究

为了进一步提高TiAl合金表面等离子喷涂MCrAlY涂层的高温氧化性能,采用激光重熔工艺对涂层进行处理,研究了激光重熔对涂层微观组织及抗氧化性能的影响.用扫描电镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)分析了涂层氧化前后的表面形貌、微观组织和相组成.结果表明:经过激光重熔处理后,涂层片层状组织得以消失,致密性提高,消除了喷涂层的大部分孔洞、夹杂等缺陷,同时使Al元素在涂层表面的重新分布,形成了Al的富集区;等离子喷涂MCrAlY层能显著提高TiAl合金的抗高温氧化性能,经过激光重熔后可进一步提高其抗高温氧化性能.     

Microstructural study and wear behavior of ductile iron surface alloyed by Inconel 617

In this research, microstructure and wear behavior of Ni-based alloy is discussed in detail. Using tungsten inert gas welding process, coating of nearly 1–2 mm thickness was deposited on ductile iron. Optical and scanning electron microscopy, as well as X-ray diffraction analysis and electron probe microanalysis were used to characterize the microstructure of the surface alloyed layer. Micro-hardness and wear resistance of the alloyed layer was also studied. Results showed that the microstructure of the alloyed layer consisted of M₂₃C₆ carbides embedded in Ni-rich solid solution dendrites. The partial melted zone (PMZ) had eutectic ledeburit plus martensite microstructure, while the heat affected zone (HAZ) had only a martensite structure. It was also noticed that hardness and wear resistance of the alloyed layer was considerably higher than that of the substrate. Improvement of wear resistance is attributed to the solution strengthening effect of alloying elements and also the presence of hard carbides such as M₂₃C₆. Based on worn surface analysis, the dominant wear mechanisms of alloyed layer were found to be oxidation and delamination.     

电子束重熔对机械合金化法制备TiC/Ti复合涂层组织及摩擦性能的影响

对机械合金化（MA）法制备的TiC/Ti复合涂层进行电子束重熔处理,分析了经过不同电子束扫描速度的重熔工艺后TiC/Ti复合涂层组织和耐磨性能的变化规律。结果表明,当扫描速度为5~15 mm/s时,重熔处理消除了MA法制备的TiC/Ti复合涂层中的孔隙和裂纹,使其硬度与耐磨性能显著提高;但扫描速度过快（20 mm/s）时,TiC/Ti复合涂层内部出现重熔导致的孔洞缺陷。随着扫描速度由5 mm/s增加至15 mm/s,重熔后TiC/Ti复合涂层中的TiC相由粗大树枝状晶体逐渐转变为弥散分布的短棒和颗粒状晶体,弥散强化作用和固溶强化作用逐渐增强,TiC/Ti复合涂层的硬度由重熔前HV 554逐渐提高至HV 783,磨损速率由5.93×10-4 mm3（N·m）-1逐渐下降至1.75×10-4 mm3（N·m）-1,扫描速度为15 mm/s重熔后TiC/Ti复合涂层的性能最佳。      

Effect of silicon content on the microstructure and properties of Fe–Cr–C hardfacing alloys

In this study, the surface of St52 steel was alloyed with preplaced powders 55Fe39Cr6C, 49Fe39Cr6C6Si, and 45Fe39Cr6C10Si using a tungsten-inert gas as the heat source. Following surface alloying, conventional characterization techniques, such as optical microscopy, scanning electron microscopy, and X-ray diffraction were employed to study the microstructure of the alloyed surface. Microhardness measurements were performed across the alloyed zone. Room-temperature dry sliding wear tests were used to compare the coatings in terms of their tribological behavior. It was found that the as-deposited coatings contained higher volume fractions of carbides (Cr₇C₃). The presence of 6%Si in the preplaced powders caused an increase in microhardness and wear resistance.     

Microstructure and wear properties of Fe–TiC surface composite coating by laser cladding

AISI 1045 steel surface was alloyed with pre-placed ferrotitanium and graphite powders by using a 5-kW CO₂ laser. In situ TiC particles reinforced Fe-based surface composite coating was fabricated. The microstructure and wear properties were investigated by means of scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, as well as dry sliding wear test. The results showed that TiC carbides with cubic or flower-like dendritic form were synthesized via in situ reaction between ferrotitanium and graphite in the molten pool during laser cladding process. The TiC carbides were distributed uniformly in the composite coating. The TiC/matrix interface was found to be free from cracks and deleterious phase. The coatings reinforced by TiC particles revealed higher wear resistance than that of the substrate.