钛合金表面激光熔覆Ni基梯度涂层的研究

为了改善Ti6Al4V钛合金表面耐磨性能和抗高温氧化性能,采用CO2激光在Ti6Al4V钛合金表面进行激光熔覆Ni基梯度涂层试验.利用扫描电镜和显微硬度计等手段分析了熔覆层组织,测试了基体和熔覆层的显微硬度.结果表明,采用适当的工艺参数,可以在钛合金表面获得连续、均匀、无裂纹和气孔的熔覆层.熔覆层组织由树枝晶和晶间共晶组织构成,并与基体形成牢固的冶金结合.由基体到表面,显微硬度过渡平稳,呈明显梯度渐变特征.     

钛合金表面三种预涂材料的激光熔覆研究

为提高钛合金的表面耐磨性能,分别以NiCrBSi、NiCrBSi B4C和B4C Ti三种材料体系为预涂粉,在Ti-6Al-4V表面涂覆不同厚度的预涂层,采用CO2激光器进行激光熔覆工艺研究.在相同激光熔覆工艺条件下,对不同材料体系的涂层质量进行观察与分析,确认NiCrBSi B4C材料涂层是三种材料体系中最好的.在激光熔覆过程中,NiCrBSi B4C材料中的B4C和Ti发生反应,原位生成增强相,对涂层有强化作用.而且,NiCrBSi的加入控制了原位反应的剧烈程度,减少裂纹和气孔,保证了涂层质量.     

Ti6Al4V合金激光原位制备TiN枝晶增强梯度复合表面层

利用连续波2kW Nd-YAG激光在Ti6Al4V合金表面原位制备TiN枝晶增强梯度金属基复合材料表面层，并研究了该表面层的显微组织和磨损性能。结果表明：该表面层沿激光熔化深度具有明显的梯度结构，表面层与Ti6Al4V基体之间呈现良好的冶金结合，Ti6Al4V的表面硬度及耐磨性得到了显著增强．     

Biocompatible and mechanical properties of low temperature deposited quaternary (Ti, Al, V) N coatings on Ti6Al4V titanium alloy substrates

A series of quaternary (Ti, Al, V) N coating layers were obtained by low temperature reactive plasma sputtering in differing deposition conditions to improve the wear resistance and the biocompatibility of a titanium surgical alloy, specifically Ti-6Al-4V. Characterization of the mechanical properties, structure and the chemical composition of the coating layer was explored by microhardness test, ball against flat wear test, scanning electron microscopy and X-ray diffraction. The biocompatibility of the optimum coating layer (as determined by mechanical performance) was examined by a modified MTT toxicity test and by monitoring cell growth assessed by quantitative stereological analysis. The experimental results are encouraging, indicating that this low temperature deposited, dense, quaternary (Ti, Al, V) N coating layer exhibits improved mechanical properties such as high hardness and excellent adhesion to a Ti alloy substrate and is highly biocompatible.     

Surface modification of titanium alloy with laser cladding RE oxides reinforced Ti3Al–matrix composites

Ti₃Al–matrix composites were prepared by laser cladding of the Al₃Ti/TiB₂/Al₂O₃ pre-placed powders on the Ti–6Al–4V alloy, which can improve the wear resistance of the substrate. With addition of the proper content of RE oxides (nano-Y₂O₃), this composite coating exhibited finer microstructure and better wear resistance. Nevertheless, excessive RE oxides could lead to the production of the micro-crack, and also decrease the temperature of the molten pool leading to the present of the un-melted TiB₂ block, which can significantly decrease the wear resistance of this composite coating.     

Effect of nano-CeO2 on microstructure properties of TiC/TiN+TiCN-reinforced composite coating

TiC/TiN+TiCN-reinforced composite coatings were fabricated on Ti–6Al–4V alloy by laser cladding, which improved surface performance of the substrate. Nano-CeO₂ was able to suppress crystallization and growth of crystals in the laser-cladded coating to a certain extent. With the addition of proper content of nano-CeO₂, this coating exhibited fine microstructure. In this study, Al₃Ti+TiC/TiN+nano-CeO₂ laser-cladded coatings have been studied by means of X-ray diffraction and scanning electron microscope. X-ray diffraction results indicated that Al₃Ti+TiC/TiN+nano-CeO₂ laser-cladded coating consisted of Ti₃Al, TiC, TiN, Ti₂Al₂₀Ce, TiC_0·3N_0·7, Ce(CN)₃ and CeO₂, this phase constituent was beneficial in increasing microhardness and wear resistance of Ti–6Al–6V alloy.     

Development of cBN reinforced Ti6Al4V MMCs through laser sintering and process optimization

In this work, a systematic study and optimization on direct metal laser sintering (DMLS) of a cBN reinforced Ti6Al4V metal matrix composite (MMC) has been carried out using the response surface methodology (RSM). Variable process parameters such as volume % of cBN (5–15%), laser power (50–60?W), scanning speed (3500–4500?mm/min), and constant parameters such as laser spot diameter (0.2?mm), hatching gap (0.2?mm), and layer thickness (0.4) were considered for the experiments. The RSM was employed to establish a regression equation to predict different output parameters of the sintered samples such as the wear rate, relative density, and microhardness. Based on the developed model, the influence of process parameters on the wear rate, density, and microhardness were accomplished with optimized results. Hence, the result, thus, obtained showed the maximum hardness and density of 519 HV_0.2 and 4.23?g/cm³, respectively, and the minimum wear of 26.49?µm in a testing time duration of 10 minutes. X-Ray Diffraction (XRD) analysis of the fabricated MMC confirms the presence of different phases such as cBN, AlN, TiN, TiB₂, and TiO₂ as a consequence of a series of chemical reactions among cBN and different elements of Ti6Al4V in an argon atmosphere.     

Effect of nano-CeO2 on microstructure properties of TiC/TiN+nTi(CN) reinforced composite coating

TiC/TiN+TiCN reinforced composite coatings were fabricated on Ti?C6Al?C4V alloy by laser cladding, which improved surface performance of the substrate. Nano-CeO₂ was able to suppress crystallization and growth of the crystals in the laser-cladded coating to a certain extent. With the addition of proper content of nano-CeO₂, this coating exhibited fine microstructure. In this study, the Al₃Ti+TiC/TiN+nano-CeO₂ laser-cladded coatings were studied by means of X-ray diffraction and scanning electron microscope. The X-ray diffraction results indicated that the Al₃Ti+TiC/TiN+nano-CeO₂ laser-cladded coating consisted of Ti₃Al, TiC, TiN, Ti₂Al₂₀Ce, TiC_0·3N_0·7, Ce(CN)₃ and CeO₂, this phase constituent was beneficial to increase the microhardness and wear resistance of Ti?C6Al?C6V alloy.     

LY12铝合金表面电火花强化层组织与性能研究

采用自制电火花强化机,以TC4合金作为电极,在空气介质中对LY12铝合金进行了表面强化。分别用扫描电镜、电子能谱分析仪与X射线衍射仪对强化层的组织、成分与结构进行了分析与研究;用显微硬度计与磨损试验机等实验设备对强化层的显微硬度与耐磨性进行了测量与分析。结果表明:强化层连续、致密,与基体之间呈冶金结合;主要由钛-铝金属间化合物和钛或铝的氮、氧化物相组成,显微硬度可达HV596;在干摩擦磨损实验条件下,强化后试样磨损体积仅为未强化试样的1/7。铝合金表面性能得到显著改善。     

TC4合金表面激光原位合成Ti／TiC生物涂层的组织结构及性能

为了提高医用TC4合金的耐磨性能,在其表面预置石墨粉,激光原位合成了Ti／TiC复合涂层,并分析了涂层的组织结构、显微硬度、耐磨性、耐蚀性及生物相容性。结果表明：涂层无气孔、裂纹等缺陷,组织为树枝晶状,显微硬度和耐磨性能较基材分别提高1倍和4．35倍,且耐蚀性及生物相容性较喷砂处理的医用TC4合金基材明显提高。     

Laser boronising of Ti–6Al–4V as a result of laser alloying with pre-placed BN

This paper discusses the effect of CO₂ laser alloying of pre-placed BN coating with Ti–6Al–4V alloy. The formation of titanium boride and titanium nitride investigated using energy dispersive X-ray diffraction (EDXRD) result were related to the microhardness and microstructure. The nitrogen and boron diffusion during the laser boronising process identified using secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectrometry (XPS) analysis was compared with the EDXRD results. The surface hardness HV1500–1700 observed at the boronised layer was five to six times higher than that of untreated Ti–6Al–4V alloy. This was compared with needle platelet and dendrite type microstructures. Theoretically estimated surface temperature values were used to interpret the compound formation in the laser alloyed layer.     

激光熔覆镍基合金层的组织与高温耐磨性能

为了改善304不锈钢工件的高温耐磨性能,利用CO2激光器在其表面熔覆了Ni基高温合金层。研究了熔覆层的物相组成、显微组织、成分分布,测试了其显微硬度、高温耐磨性能等,并与基材进行了对比。结果表明:Ni基合金熔覆层的组织从熔池底部到表层为胞状晶—柱状枝晶—树枝晶;熔覆层的主要组成相是Ni3Cr2,NbC,Mo2C与Cr23C6;Ni基合金粉末中添加难熔元素Cr,Mo,Nb等对熔覆层的组织起到了固溶强化、硬质相强化和弥散强化作用;熔覆层的平均显微硬度达到了405 HV,高温耐磨性能是基体的2倍多。     

Ti-SiC Composite and TiC Ceramic Layer Formation on Ti6Al4V Surface by Laser Alloying of Pre-Placed SiC Coating

The Ti-6Al-4V alloy pre-placed with SiC coating was laser alloyed using high power CO2 laser. The laser alloyed cross section shows dendrite and Ti-SiC composite layer microstructure and the respective hardness was 650–800 HV and 1500–2000 HV. The observed hardness was 2 to 7 times greater than that measured on the bulk Ti-6Al-4V substrate. The laser alloyed surface produced high temperature ceramic phases such as TiC, TiSi and Ti5Si3. The elemental analysis was qualitatively estimated using SIMS analysis.     

A novel Ti cored wire developed for wire-feed arc deposition of TiB/Ti composite coating

A novel Ti cored wire containing TiB2,Al60V40 and Ti6Al4V mixed powders was developed for wire-feed arc deposition of TiB/Ti composite coating,to enhance the hardness and wear resistance of Ti alloy.Results showed that after experiencing several chemical reactions,the wire was melted in the arc zone and turned into nonuniform droplets composed of Ti-Al-V-B melt and undecomposed TiB2 particles.With the increase of welding current,the detachment time of droplet shortened while the transfer frequency accelerated,accompanied by the improvement in coating surface quality.The spatial distribution of TiB whiskers in coating was governed by welding current.A uniform distribution could be achieved as welding current was sufficient at the expense of elevated dilution ratio,while increasing wire feeding speed could compensate the dilution loss of TiB whisker to some extent.The decomposition process of TiB2 particles and the microstructure evolution mechanism of coating was discussed in detail.The optimum coating possessed uniform microstructure,relatively low dilution ratio,and high hardness(639.1 HV0.5)as compared with Ti6Al4V substrate(326 HV0.5).Indentation morphology analysis verified the excellent performance was ascribed to the load-sharing strengthening of TiB whiskers.This study provides a high-efficiency fabrication method for the ever-developing titanium matrix composites(TMCs)coating.     

In situ synthesis of TiN/Ti3Al intermetallic matrix composite coatings on Ti6Al4V alloy

The aim of this paper was to develop an in situ method to synthesize the TiN reinforced Ti₃Al intermetallic matrix composite (IMC) coatings on Ti6Al4V alloy. The method was divided into two steps, namely depositing pure Al coating on Ti6Al4V substrate by using plasma spraying, and laser nitriding of Al coating in nitrogen atmosphere. The microstructure and mechanical properties of TiN/Ti₃Al IMC coatings synthesized at different laser scanning speeds (LSSs) in laser nitriding were investigated. Results showed that the crack- and pore-free IMC coatings can be made through the proposed method. However, the morphologies of TiN dendrites and mechanical properties of coatings were strongly dependent on LSS used in nitriding. With decreasing the LSS, the amount and density of TiN phase in the coating increased, leading to the increment of microhardness and elastic modulus and the decrement of fracture toughness of coating. When the LSS was extremely high (i.e., 600 mm/min), only a thin TiN/Ti₃Al layer with thickness around of 100 μm was formed near the coating surface.     

Dissolution precipitation mechanism of TiC/Ti composite layer produced by laser cladding

Abstract

TiC reinforced Ti matrix composite layer was fabricated by laser cladding of Ti and TiC powder mixture on Ti–6Al–4V alloy. Dissolution precipitation mechanism was speculated to illustrate the formation of TiC dendrite in the composite layer. Microstructure evolution of the composite layer has been explained by this mechanism. The composite incorporates the advantages of external particle composites and in situ synthesised particle composites. This mechanism offers an alternative novel idea for the design of bulk composites as well as composite layers. The composite layer exhibits high hardness and excellent wear resistance.     

Evaluation of the effects of plasma nitriding temperature and time on the characterisation of Ti 6Al 4V alloy

The effects of plasma nitriding (PN) temperature and time on the structural and tribological characterisation of Ti 6Al 4V alloy were investigated. PN processes under gas mixture of N₂/H₂ = 4 were performed at temperatures of 700, 750, 800 and 850 °C for duration of 2, 5 and 10 h. Cross section and surface characterisation were evaluated by means of SEM, AFM, XRD and microhardness test techniques. Dry wear tests were performed using a pin on disc machine. Mass loss and coefficient of friction were measured during the wear tests. Three distinguished structures including of a compound layer (constituted of δ-TiN and ɛ-Ti₂N), an aluminium-rich region and a diffusion zone (interstitial solid solution of nitrogen in titanium) were detected at the surface of plasma nitrided Ti 6Al 4V alloy. These structures increased surface hardness of Ti 6Al 4V alloy significantly and gradually distributed the hardness from the surface to the substrate. The "surface hardness", "surface roughness", "wear resistance" and "coefficient of friction" of the alloy were increased due to plasma nitriding process. Moreover, rising both process temperature and time led to increasing of "layers thicknesses", "surface hardness", "surface roughness", "dynamic load-ability" and "wear resistance" of Ti 6Al 4V alloy.     

Wear behaviors of an (TiB + TiC)/Ti composite coating fabricated on Ti6Al4V by laser cladding

A titanium-based composite coating reinforced by in situ synthesized TiB whiskers and TiC particles was successfully fabricated on Ti6Al4V by laser cladding. The coating is mainly composed of α-Ti cellular dendrites and a eutectic in which a large number of needle-shaped TiB whiskers and a few equiaxial TiC particles are uniformly embedded. The wear resistance of the coating is significantly superior to that of Ti6Al4V under the dry sliding wear condition at room temperature.     

The effect of different methods to add nitrogen to titanium alloys on the properties of titanium nitride clad layers

In this investigation, titanium nitride (TiN) reinforcements are synthesized in situ on the surface of Ti–6Al–4V substrates with gas tungsten arc welding (GTAW) process by different methods to add nitrogen, nitrogen gas or TiN powder, to titanium alloys. The results showed that if nitrogen gas was added to titanium alloys, the TiN phase would be formed. But if TiN powder was added to titanium alloys, TiN + TiN_x dual phases would be presented. The results of the dry sliding wear test revealed that the wear performance of the Ti–6Al–4V alloy specimen coated with TiN or TiN + TiN_x clad layers were much better than that of the pure Ti–6Al–4V alloy specimen. Furthermore, the evolution of the microstructure during cooling was elucidated and the relationship among the wear behavior of the clad layer, microstructures, and microhardness was determined.     

Ti6Al4V合金激光原位合成自润滑复合涂层高温摩擦学性能

为提高Ti6Al4V合金的高温摩擦学性能,采用激光熔覆技术在其表面原位合成多相混杂金属基高温自润滑耐磨复合涂层,熔覆粉末的成分为Ni60-16.8%TiC-23.2%WS_2(质量分数,下同),系统地研究复合涂层的显微组织、物相结构及其在20,300,600,800℃下的摩擦学性能和相关磨损机理。结果表明:复合涂层的显微硬度(701.88HV_0.5)约为基体(350 HV_0.5)的2倍;由于原位合成固体润滑相(Ti_2SC/TiS/NiS/TiO/TiO_2/NiCr_2O_4/Cr_2O_3)和硬质相(W,Ti)C_1-x/TiC/Cr_7C_3的协同作用,复合涂层的耐磨减摩性能明显优于基体。随着温度升高,涂层和基体的摩擦因数和磨损率均呈下降趋势,在800℃时复合涂层和基体的摩擦因数分别为0.32和0.43,磨损率分别为1.80×10^-4,2.92×10^-5mm/Nm。在800℃下塑性变形、分层和氧化磨损为基体主要磨损机理,复合涂层以氧化磨损和轻微的黏着磨损为主。