TC4钛合金表面激光熔覆WC增强镍基复合涂层的组织及耐磨性

为提高TC4钛合金的耐磨性,利用激光熔覆技术(laser cladding,LC)在TC4钛合金表面制备Ni60+50%WC(体积分数)和deloro22(d22)粉末打底+(Ni60+50%WC)2种耐磨复合涂层。采用扫描电子显微镜(SEM)、能谱仪(EDS)以及X射线衍射仪(XRD)来表征涂层的微观结构和物相组成;使用HV-1000显微维氏硬度计、HRS-2M型高速往复摩擦磨损试验机和WDW-100D电子万能试验机来分析涂层的性能。结果表明:2种涂层均由W₂C、TiC、Ni₁₇W₃、Ni₃Ti和Ti_xW_1-x相组成,2种涂层不仅与基体呈现出优异的冶金结合,而且组织均匀致密,没有裂纹瑕疵;由于涂层中存在着原位合成的硬质相和细晶强化共同作用使得涂层硬度显著提高,约为TC4基体的2.82倍;2种涂层的摩擦系数(COF)和磨损量都远低于TC4钛合金基体;Ni60+50%WC复合涂层和d22粉末打底+(Ni60+50%WC)复合涂层的抗剪切结合强度分别为188....     

Laser cladding of continuous caster lateral rolls: Microstructure,wear and corrosion characterisation and on-field performance evaluation

Laser cladding has been used to improve the service life of lateral rolls which experience high temperature wear and corrosion in the zero segment zone of continuous slab caster. Three different compositions of nickel base powders with varying chromium, molybdenum, boron and niobium content with different wear and corrosion resistance properties have been used as cladding consumables. The microstructure of the clad layers shows a two phase cellular dendritic structure, with nickel–chrome dendrites surrounded by hard phases rich in chromium and boron or niobium. Hard precipitates contribute to wear resistance whereas the presence of chromium along with molybdenum in nickel-rich matrix improves resistance to corrosion. Actual performance results suggest that the powder material with higher wear resistance property gives the maximum life when the corrosion conditions are less hostile. In rolls cladded with highest boron and nickel containing powders, the layers were intact, whereas fine cracks and de-lamination was observed in the other rolls.     

Microstructure and wear resistance of TaC reinforced Ni-based coating by laser cladding

The in situ synthesized TaC particulate reinforced Ni-based composite coating was fabricated on a mild steel by laser cladding of powder mixture of Ni60 alloy powder with (Ta₂O₅ + C)-doping. The microstructure and wear resistance of the TaC/Ni60 composite coating were investigated. It is shown that the coating is bonded metallurgically to the substrate and has a homogeneous fine microstructure containing both approximate cubic TaC particle and acicular chromium carbide uniformly dispersed in the dual phase matrix of γ(Ni) solid solution and eutectic of Cr₃C₂, Fe₂B with γ(Ni). Compared to a Ni60 coating, the hardness of the TaC/Ni60 composite coating was enhanced by a factor of 1.38, could achieve a Vicker microhardness of Hv_0.31100. And the wear rate in a block on ring test against hardened steel was reduced by a factor of five. This is attributed to the presence of in situ synthesized TaC particles and their well distribution in the coating.     

Laser surface coating of Fe-Cr-Mo-Y-B-C bulk metallic glass composition on AISI 4140 steel

Fe-based bulk metallic glasses exhibit very high hardness, elastic modulus/limit and wear/corrosion resistance. In the present investigation, an attempt has been made to develop an amorphous coating with Fe₄₈Cr₁₅Mo₁₄Y₂C₁₅B₆ bulk metallic glass on AISI 4140 substrate by laser surface processing. Following coating, the microstructure and phase aggregate were analyzed by scanning electron microscope and X-ray diffraction, respectively. Microhardness and wear resistance were assessed using Vickers microhardness tester and ball-on-plate wear testing machine, respectively. The coating thickness varied directly with incident laser power and interaction time. Despite trials with wide range of process parameters, the present experiments were unable to retain complete amorphous surface microstructure after laser surface coating. Numerical prediction of the thermal profile and related parameters suggest that the cooling rate and thermal gradient experienced by the coated zone were fairly high. Yet failure to retain amorphous/glassy microstructure of an otherwise bulk metallic glassy alloy suggests that compositional changes (solute redistribution) within the coated zone and across the coating-substrate interface are responsible for nucleation and growth of crystalline phases from the melt. However, correlation between coating parameters and surface microstructure and properties allowed determination of the optimum conditions that ensured fine grained uniform microstructure with a significant improvement in hardness and wear resistance.     

激光熔覆纳米TiC增强AlCoCrFeNi高熵合金磨损及腐蚀性能研究

采用激光熔覆技术在 304 不锈钢表层制备了纳米 TiC 增强 AlCoCrFeNi 高熵合金涂层,利用扫描电镜、能谱仪、X 射线衍射仪等设备系统研究了涂层的组织形貌、相结构及元素分布;采用显微硬度计、摩擦磨损仪、超景深显微镜和电化学工作站等设备表征了涂层的硬度分布、磨损特性及耐腐蚀性能。结果表明,类球形纳米级 TiC 与棒状微米级 TiC 沉淀相均匀分布在涂层 bcc（B2）相基体中。添加 TiC 增强相后,AlCoCrFeNi 高熵合金涂层的硬度比未添加 TiC 涂层的硬度提升了 15%;表层磨损率及磨损后表面单位面积粗糙度（Sa）分别较 AlCoCrFeNi 高熵合金涂层降低了 42% 和 18%,涂层中 TiC 增强相的弥散强化作用是涂层硬度、耐磨性提升的主要原因。添加 TiC 的 AlCoCrFeNi 高熵合金涂层较未添加 TiC 涂层的自腐蚀电流降低了约1个数量级,TiC 增强相使涂层表面形成致密的钝化膜是其耐蚀性能好的主要原因。     

纳米CeO2/Co基合金复合材料激光熔覆层组织与耐磨性研究

研究了纳米CeO2对Co基合金激光熔覆层宏观质量、显微组织、相结构和性能的影响。采用OLYMPAS-PME3显微镜、PHILIP XL30扫描电镜和XD-3A型衍射仪分析了熔覆层的显微组织和相结构,利用MM-200环-块滑动磨损试验机及JSM-35C型扫描电镜检测了熔覆层的耐磨性和分析了其磨损机理。结果表明:纳米CeO2的加入能使Co基熔覆层表面平整而无气孔和裂纹,使熔覆层的宏观质量得到改善;纳米CeO2在熔覆层中能够细化组织,并且可以抑制树枝晶的生长,促使熔覆层形成了等轴晶;添加纳米CeO2后不仅有新相CeCo2产生,并且一部分-γCo转变为-εCo相。在2.0 kW功率下加入1.5%纳米CeO2时熔覆层的相对耐磨性最好,熔覆层由磨粒磨损和黏着磨损转变为微动磨损,过量的CeO2加入,反而降低耐磨性。     

激光熔覆FeCrNiCoMnBx高熵合金涂层的组织结构与性能

采用激光熔覆技术制备FeCrNiCoMnB_x高熵合金涂层,研究了硼含量对激光熔覆FeCrNiCoMnB_x高熵合金涂层的组织结构、硬度和摩擦磨损性能的影响,以及硼化物中层错形成机制。结果表明:涂层均由简单fcc结构固溶体和硼化物两相组成。当硼含量x≤0.75时,生成的硼化物以(Cr,Fe)_2B相为主;而当硼含量x=1时,生成大量的(Fe,Cr)_2B相。随着硼含量的增加,涂层中的硼化物含量增加,硬度增大,耐磨性能增强。硼化物(Fe,Cr)_2B相在(110)面存在大量堆垛层错。硼化物中的层错是(Fe,Cr)_2B相通过(110)面的层错(滑移距离为1/4[111])方式而向(Cr,Fe)_2B相转变而产生。     

Microstructure and wear properties of TiC/FeCrBSi surface composite coating prepared by laser cladding

Titanium carbide particles reinforced Fe-based surface composite coatings were fabricated by laser cladding using a 5 kW CO₂ laser. The microstructure, phase structure 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 were formed via in situ reaction between ferrotitanium and graphite in the molten pool during the laser-clad process. The morphology of TiC is mainly cubic and dendritic form; and the TiC carbides were distributed uniformly in the composite coating. The TiC/matrix interface was found to be free from cracks and deleterious phases. The coatings reinforced by TiC particles revealed higher wear resistance and lower friction coefficient than that of the substrate and FeCrBSi laser-clad coating.     

退火对激光熔覆AlCoCrFeNiTi0.5高熵合金涂层组织和耐磨性的影响

对激光熔覆AlCoCrFeNiTi_0.5高熵合金涂层进行900℃退火,保温5h处理。主要对退火前后样品的微观结构和耐磨性进行研究。XRD结果表明,退火后的AlCoCrFeNiTi_0.5高熵合金涂层,其相组成有Co₃Ti和BCC结构的AlFe固溶相,出现典型的成分均匀的网状调幅分解组织;退火后的平均显微硬度达到989HV_0.5,比退火前提高了73.5%;耐磨性测试结果显示,退火后磨损量比退火前降低了92.5%,磨损宽度是退火前的50%。     

喷射成形过共晶Al-Si合金的组织特征和磨损行为

采用喷射成形技术制备了过共晶Al-Si耐磨合会,分析了合金的显微组织结构,利用M200磨损试验机对喷射成形和铸造Al-Si合金的耐磨性和磨损失效形式进行了分析比较。结果表明：喷射成形能够显著改变过共晶Al-Si合金中初晶Si相的形态和尺寸,细化合金的基体组织;与普通铸造合金相比,具有更好的耐磨性能。     

Microstructure and high-temperature wear behavior of laser clad Ni-Ti-Si ternary metal silicide coatings

Ni-Ti-Si ternary metal silicide coatings were fabricated on AISI 304 stainless steel by laser cladding process. The coatings consisted of Ni₁₆Ti₆Si₇ primary dendrite and interdendritic Fe-Ni-based solid solution γ and exhibited excellent abrasive and adhesive wear resistance under high temperature metallic dry sliding wear conditions. The excellent wear properties were attributed to the high hardness and covalent dominant atomic bond of the metal silicide Ni₁₆Ti₆Si₇. The dominant wear mechanism of the coating were delamination of the coating and material transfer from the mating surface.     

Fragility and glass forming ability of Al-Ni-Ce alloy melts

The fragility of Al-Ni-Ce alloy melts with three kinds of different compositions, Al85Ni10Ce5,Al85Ni8Ce7, Al85Ni5Ce10 (mole fraction, %), was studied using oscillating-vessel viscometer and differential scanning calorimetry. Their fragility parameters obtained from experiments and theoretic calculation are: 238, 228 and 335 respectively. The results indicate that these three kinds of Al-Ni-Ce alloy melts are very fragile liquids, which kinetically show strong non-Arrhenius behaviour in the Angell plot, so they have poor glass forming ability (GFA).The alloy melt AI85NiSCe10 has the largest fragility parameter among the three alloy melts. In the preparation of rapidly quenched amorphous ribbons, AI85Ni10Ce5 and AI85Ni8Ce7 can gain amorphous ribbons when the rotate speed of the roller reaches 800r/min, while for Al85Ni5Ce10 it must exceed 1 000r/min.     

Microstructure and wear property of laser-clad Co3Mo2Si/Coss wear resistant coatings

Novel wear resistant Co₃Mo₂Si/Co_ss coatings consisting of a microstructure of hard and strong Co₃Mo₂Si intermetallic phases embedded in the ductile Co-base matrix were fabricated on austenite stainless steel by the laser cladding process from the Co-Mo-Si powder blend precursor. The microstructures of the coatings were characterized by optical microscopy (MO), X-ray diffraction (XRD), and scanning electron microscopy (SEM) with an energy-dispersive X-ray analysis (EDX). The wear resistance of the coatings was evaluated in a dry sliding wear test condition at room temperature. Results indicated that the laser-clad Co₃Mo₂Si/Co_ss coatings exhibited very excellent wear resistance against abrasive and adhesive wear.     

Microstructure and mechanical properties of a spray-formed Ti-based metallic glass former alloy

A Ti_45.8Zr_6.2Cu_39.9Ni_5.1Sn₂Si₁ composite plate was spray deposited on a copper substrate. From the bottom substrate-contact surface to the upper free surface of the deposit, a layered microstructure evolution in the order of fully amorphous (for the region 1-2 mm perpendicularly away from the substrate), amorphous/nanocrystalline (3-4 mm from the substrate), ultrafine-grained crystalline (5-6 mm from the substrate) and micron-sized crystalline phases (7-8 mm from the substrate) was observed. The oversprayed powders bellow 50 μm exhibit fully amorphous structure, while the ones above 50 μm show certain crystallization behavior. The fracture strength of 1.58-1.85 GPa with obvious plastic strain can be achieved under compressive tests for the spray-formed deposit. Spray forming can therefore produce bulk-sized high strength Ti-based alloy which evolves gradually from certain non-equilibrium towards equilibrium during deposition, which were considered to be attributable to the chill effect at the bottom substrate-contact surface and the following heat entrapment from the successively deposited droplets or powders.     

Influence of powder size on the crystallization behavior during laser solid forming Zr55Cu30Al10Ni5 bulk amorphous alloy

The Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glasses (BMGs) were prepared using laser solid forming (LSF) process from the plasma rotating electrode process (PREP) powder. The effect of the powder size on the crystallization behavior of the remelted zone (RZ) and heat affected zone (HAZ) was investigated. It was found that the as-prepared powders were composed of the amorphous phase and Al₅Ni₃Zr₂-type phase. The RZ mainly kept the amorphous state after LSF. The residual Al₅Ni₃Zr₂-type phase could be observed in RZ only if the powder size was larger than 106 μm. Meanwhile, the NiZr₂-type nanocrystals at the boundary of RZ primarily formed from the solidification of remelted liquid. With the increase of the powder size, the lower overheating temperature and shorter existing time of the molten pool enhanced the heredity of Al₅Ni₃Zr₂ clusters and other intermetallic clusters in remelted alloy melt, which decreased the thermal stability of the already-deposited layer. The volume fraction of crystallization in the deposit increased with the increase in powder size. There was no crystallization occurred in the HAZ between the adjacent tracks and layers for the deposit prepared by the powder with the size range of 53–75 μm. However, the wide crystalline band with Al₅Ni₃Zr₂-type faceted phase, CuZr-type dendrite, CuZr₂-type spherulite and NiZr₂-type nanocrystal were observed in the entire HAZ for the deposit prepared by the powder with the size range of 106–150 μm. The finer powder was benefit to prepare the BMGs by LSF.     

Fragility and thermal stability of Pt- and Pd-based bulk glass forming liquids and their correlation with deformability

The fragility parameter m of (Pt or Pd)–(Ni, Cu)–P bulk metallic glasses (BMGs) was characterized and compared to other systems. The results indicate that the Pt₆₅Ni₁₅P₂₅ alloy is the most fragile and thermally stable at the supercooled liquid state, thus is the most workable among the presently developed BMGs. To express the degree of workability, a deformability is introduced then correlated with m and the reduced thermal stability . A master curve in term of and has been established for various BMGs, d^* thus can be uniquely related to .     

Low temperature heat capacity and electrical resistivity of the Ti40Zr25Cu12Ni3Be20 glass forming alloy

Gaining knowledge of electronic structure provides useful information for understanding unique properties of metallic glasses. In this study, low temperature heat capacity and electrical resistivity of the glass forming Ti₄₀Zr₂₅Cu₁₂Ni₃Be₂₀ alloy with glassy, quasicrystalline, or crystalline states below 300 K were investigated. The precipitation of the I-phase was revealed in the initial crystallization process of the Ti₄₀Zr₂₅Cu₁₂Ni₃Be₂₀ BMG. The glassy state has higher state density at Fermi level than its quasicrystalline or crystalline counterparts, which could be interpreted by the electron localization in glassy state as well as a pseudo-Brillouin zone formed nearby Fermi surface in the quasicrystalline state. None of the three states showed superconductivity phenomenon down to 1.9 K. Temperature dependence of resistivity for both the glassy state and the quasicrystalline state exhibited negative temperature coefficient and was less sensitive to temperature than the crystalline state. The electrical resistivity showed a smaller value for the I-phase than that for the glass due to lower structural integrity of I-phase. Electrical resistivity as well as heat capacity measurements indicated that the electronic structure of the quasicrystalline state is quite similar to glassy state but far from crystalline state.     

Friction and wear of MoS2 films on laser textured steel surfaces

Incorporation of solid lubricant into micro-reservoirs produced by Laser Surface Texturing (LST) and its effect on the tribological properties of surfaces under dry friction is studied. The density of the dimple reservoirs and the height of the bulges around them are investigated in terms of the longevity of solid lubricant films burnished on LST steel surfaces. Friction tests were performed using a ball-on-flat device. Optimum density (40-50%) of the dimples is revealed. It is shown that the adhesion of solid lubricant in the space between the dimples is provided by mechanical engagement of particles in the rough surface and by smearing the solid lubricant around the dimples. Best results are obtained with the surfaces that were lapped to half of the height of bulges. Long wear life of burnished film on LST steel surfaces is apparently provided by preservation of thin MoS₂ film around the bulges and by supply of solid lubricant from the dimples to the surface.     

Microstructure and wear performance of gradient Ti/TiN metal matrix composite coating synthesized using a gas nitriding technology

Surface modification is an attractive method to enhance the surface hardness and wear resistance of titanium. In this paper, a continuous wave 2 kW Nd:YAG laser was used to synthesize Ti/TiN metal matrix composite coating on the surface of commercial pure titanium. The microstructure and the wear resistance of the synthesized metal matrix composite coating were investigated. The synthesized surface Ti/TiN metal matrix composite coating had a pronounced gradient microstructure through the melt depth. Good metallurgical bonding between the reinforcing phase of the metal matrix composite and the titanium matrix was observed. The hardness and wear resistance under block-on-ring dry sliding wear testing conditions of the synthesized Ti/TiN metal matrix composite coating were markedly enhanced.