In situ laser surface coating of TiC metal-matrix composite layer

Surface alloys are of great interest for improving the mechanical and/or chemical properties of the near-surface region on metallic materials. A new method, in situ laser surface coating of metal-matrix composite, is described, by which to produce a surface composite layer. Using this process, -Ni-TiC _x composite surface layers were achieved on mild steel; they exhibited increased hardness, and in situ formed TiC_x particles, 0.5–0.8 m in size, were homogeneously distributed in the top half of the matrix layer.     

High-temperature thermal barrier coating formation by laser alloying of CP-Ti with pre-placed Ni-SiC coating

High-temperature thermal barrier coating was created on CP-Ti using a pre-placed Ni-SiC layer by laser alloying technique. The coating was developed using 80% Ni + 20% SiC, 50% Ni + 50% SiC and 60% Ni + 40% SiC, and the latter two compositions are found to be efficient in producing a uniform layer. The 100% SiC pre-placement was also used. A flaw-less coating of 0.4–0.6 mm thickness was produced at a lower power density of 1.3 to 1.9 × 10⁵ W cm^–2. Very high power density of 2.5–3.0 × 10⁵ W cm^–2 is inefficient to produce uniform coating. The laser alloyed coating consists of dendrites and intermetallic precipitates. The degree of dendrite population depends upon the coating composition and laser processing conditions. The coating hardness was 600–1200 HV, which is three to six times higher than the base titanium. Uniform hardness was obtained for the coatings produced at a laser power density of 1.3 × 10⁵ W cm^–2. The titanium silicide (TiNiSi, Ti₅Si₃, TiSi) and nickelide (NiTi₂) phases formed on the laser-alloyed coating surface was confirmed by X-ray analysis. These intermetallic phases can improve high-temperature properties of titanium and its alloys. The effect of laser power density and coating composition on the alloying depth alloying width, hardness and microstructure are discussed. The present work investigated the microstructure evolution, hardness and compound phases by means of optical and scanning electron microscopy, Vickers hardness testing, EDXRD and SIMS analysis. A 5 kW CW CO₂ laser was used for laser alloying experiments.     

Mechanism of formation of hot gas sprayed coatings on SCh-20 cast iron

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 2, pp. 110–113, March–April, 1990.     

In situ synthesis of TiC composite for structural application

In situ TiC reinforced Al composite has been synthesized from the reaction between Ti and activated carbon. The size of in situ TiC is in the range from sub-micron to a maximum of 1.7 μm. Degree of reaction between Ti and activated carbon increases with increasing reaction temperature and amount of carbon. At low reaction temperature, the tensile strength of the composite is low as a result of the presence of unreacted activated carbon retained in the material. The retained carbon can be reduced by increasing reaction temperature. It has been observed that at low reaction temperature formation of Al₃Ti is a dominant phenomenon while at high reaction temperature Al₃Ti is not stable. Along with its disappearance, formation of TiC becomes favorable.     

Creep rupture behaviors of a laser melting deposited TiC/TA15 in situ titanium matrix composite

The creep rupture behaviors of a laser melting deposited in situ TA15 titanium matrix composite reinforced by 10.8 vol.% TiC particulates were investigated at 873 and 923 K. The as-deposited TiC reinforcements were mainly in near-equiaxed and coarse dendritic with a stoichiometry of TiC_0.71. The composite exhibited a superior creep resistance to the monolithic titanium alloy. The creep rupture mechanism was dominated by a mixture of particle cracking, interface debonding and interparticle voiding. Voids nucleated at broken particles, debonded interfaces and interparticle matrix at the initial stage of rupture. The growth, coalescence and transverse linkage of these voids through the matrix contributed to the final failure of the composite. The strengthening in creep resistance of the composite was mainly attributed to the load transfer from the matrix to the particle reinforcements and the refinement of the Widmanstätten matrix.     

激光熔覆制备原位自生TiC增强Ni3（Si,Ti）复合涂层研究

运用激光熔覆技术修复受损的烟汽轮机叶片,在GH864镍基合金表面制备原位自生TiC颗粒增强Ni3(Si,Ti)金属间化合物复合涂层.利用扫描电镜、能谱分析仪、X射线衍射仪及显微硬度计研究了(Ti+C)的加入量对熔覆层组织及硬度的影响.研究表明:在优化的工艺参数下可获得宏观质量完好,无裂纹、气孔等缺陷,且与基体呈冶金结合的激光熔覆层,熔覆层由Ni(Si)、Ni3(Si,Ti)和TiC组成;当合金粉末中(Ti+C)的加入量为20%时熔覆层的硬度最高可达780Hv,是基体材料的2.4倍.     

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.     

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.     

Microstructure and thermal behaviour of plasma sprayed zirconia/alumina composite coating

In thermal barrier coatings (TBC), failure occurs near or at the interface between the metallic bondcoat and topcoat. On high temperature conditions, an oxide scale which is named thermally grown oxide (TGO) occurs along the bond/topcoat interface. For diminishing the creation of TGO, a dense coating with low residual stress and thermal stress buffer layer was preferable. High hardness ceramic coatings could be obtained by gas tunnel type plasma spraying, and the deposited coating had superior property in comparison with those deposited by conventional type plasma spray method. In this study, the gas tunnel type plasma spraying system was utilized to produce a zirconia/alumina functionally graded thermal barrier coating and discussed its physical and mechanical properties, thermal behavior and high temperature oxidation resistance of the coating are discussed. Consequently, the proposed system exhibited superior mechanical properties and oxidation resistance at the expenses of a slightly lower thermal insulating effect. This interlayer is preferred in order to minimize the detrimental effect of the phase transformation of gamma-Al2O3 to alpha-Al2O3.     

In situ synthesis of hydroxyapatite-grafted titanium nanotube composite

ABSTRACT

The present study is an investigation to demonstrate the effectiveness of in situ approach in the synthesis of hydroxyapatite-grafted titanium nanotube composite (HA-TNT). This method involves combining the process of HA sol–gel and rapid breakdown anodisation of titanium in a novel solution consisting of NaCl and N₃PO₄. This new synthesis approach produced a uniform dispersion of Anatase and Rutile phases of TiO₂ nanotubes with minimal agglomeration in the matrix of crystalline HA. The characterisation of homogenised HA-TNT composite was investigated via field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM) and X-ray diffraction (XRD). FESEM and TEM images indicated the nanostructure of composite with TiO₂ nanotube diameter of approximately 10 nm. XRD and EDS analyses confirmed the formation of HA crystalline with the Ca/P ratio of 1.58 and formation of Anatase and Rutile phase of TiO₂ nanotubes.     

Adhesion behavior of plasma sprayed thermal barrier coatings on Al-6061 and cast iron substrates

In this work an investigation was carried out on adhesion strength and micro-hardness of plasma sprayed coatings on Al-6061 and cast iron substrate materials. For the adhesion test, ASTM C633, and for the micro hardness, ASTM E384 standards were used. From the results obtained it was found that the main failure locations were in the bond coat-substrate interface, which is considered as adhesion strength. The various parameters affecting adhesion strength are also discussed.     

Growth morphology and mechanism of primary TiC carbide in laser clad TiC/FeAl composite coating

TiC-reinforced FeAl intermetallic matrix composite (IMC) coatings were fabricated on substrate of 1Cr18Ni9Ti stainless steel using laser cladding. X-ray diffraction (XRD) was used to identify the phases in the laser clad composite coating and the growth morphologies of TiC carbide were observed by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results showed that there are two phases in the laser clad composite coating: TiC and FeAl intermetallic matrix alloy. The primary TiC carbide in laser clad coating nucleates heterogeneously on the surface of oxide particles; its growth morphology is found to be in a unique radial-branching dendrite with strongly faceted feature. The growth mechanism of TiC is confirmed to be lateral growth from the ledges or steps existing on the growing fronts.     

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。      

基于CO2激光热效应的喷塑涂层界面结合强度研究

用CO2脉冲激光扫描AISI304-喷塑涂层的表面,分析喷塑涂层的破坏特征和断裂行为,研究了激光热效应下喷塑涂层的结合强度.结果表明,可用吸收的激光能量定量地表征涂层和基体之间的结合强度,聚烯烃喷塑涂层-AISI304的理论结合强度为19.9 MPa,当涂层中塑料与基体的溶度参数相近时,涂层与基材的结合界面附着力较强.     

Microstructures and wear properties of in situ formed composite coatings produced by laser alloying technique

Laser-surface alloying of titanium alloy Ti-6Al-4V with C and Si mixed powders has been carried out. The composite coatings, thickness of about 0.7 mm, mainly consisting of titanium carbides and silicides, have a hardness of about 1500 HV_0.1, and the wear resistance is 4 times more than that of the as-received.