Phase constituents and microstructure of laser cladding Al2O3/Ti3Al reinforced ceramic layer on titanium alloy

Laser cladding of the Fe₃Al + TiB₂/Al₂O₃ pre-placed alloy powder on Ti-6Al-4V alloy can form the Ti₃Al/Fe₃Al + TiB₂/Al₂O₃ ceramic layer, which can greatly increase wear resistance of titanium alloy. In this study, the Ti₃Al/Fe₃Al + TiB₂/Al₂O₃ ceramic layer has been researched by means of electron probe, X-ray diffraction, scanning electron microscope and micro-analyzer. In cladding process, Al₂O₃ can react with TiB₂ leading to formation of amount of Ti₃Al and B. This principle can be used to improve the Fe₃Al + TiB₂ laser cladded coating, it was found that with addition of Al₂O₃, the microstructure performance and micro-hardness of the coating was obviously improved due to the action of the Al-Ti-B system and hard phases.     

Cu + TiB2 composite filler for brazing Al2O3 and Ti-6Al-4V alloy

Al₂O₃ and Ti-6Al-4V alloy were brazed using Cu + TiB₂ composite filler, which manufactured by mechanical milling of Cu and TiB₂ powders. Typical interface microstructure of joint was Al₂O₃/Ti₄(Cu,Al)₂O/Ti₂Cu + Ti₃Al + Ti₂(Cu,Al)/Ti₂(Cu,Al) + AlCu₂Ti/Ti₂Cu + AlCu₂Ti + Ti₃Al + Ti₂(Cu,Al) + TiB/Ti(s.s) + Ti₂Cu/Ti-6Al-4V alloy. Based on temperature- and time-dependent compositional change, the formation of intermetallics in joint was basically divided into four stages: formation of interfacial Ti₄(Cu,Al)₂O in Al₂O₃ side, formation of Ti₂Cu, Ti₃Al, TiB, Ti₂Cu, and AlCu₂Ti in layers II and IV, formation of Ti₂(Cu,Al) and AlCu₂Ti in layer III, formation of Ti + Ti₂Cu hypereutectoid organization adjacent to Ti-6Al-4V alloy. TiB in situ synthesized in joint not only acted as low thermal expansion coefficient reinforcement to improve the mechanical properties at room temperature, but also as skeleton ceramic of joint to increase high temperature mechanical properties of Al₂O₃/Ti-6Al-4V alloy joint increasing. When the joint containing 30 vol.% TiB brazed at 930 °C and 10 min of holding time, the maximum room temperature shear strength of joint was 96.76 MPa, and the high temperature shear strength of joint was 115.16 MPa at 800 °C.     

AZ91D镁合金表面激光熔覆Al-TiC涂层组织和性能的研究

目的研究Al-TiC涂层组织和性能的特性,以提高镁合金涂层的硬度和耐蚀性能。方法采用Nd:YAG固体激光器,在AZ91D镁合金表面通过激光熔覆制备Al-TiC涂层,采用光学显微镜、X射线衍射仪、显微硬度计、电化学工作站,对熔覆层的组织形貌、物相结构、显微硬度和耐蚀性能进行测定和分析。结果 Al-TiC涂层的主要组成相有AlTi_3(C,N)_(0.6),Al_3Mg_2,Mg_2Al_3,Al和TiC等。激光熔覆层的厚度约为0.35 mm,表面成型良好,结合层晶粒细小,熔覆层与镁合金基体之间结合良好,呈大波浪形。熔覆层试样的平均显微硬度为224HV,约为基体显微硬度(62HV)的4倍,由此表明熔覆层对镁合金硬度有明显的增强作用。镁合金基体的自腐蚀电位为-1.475 V,自腐蚀电流密度为7.556×10~(–5) A/cm~2,熔覆层试样的自腐蚀电位为-1.138V,自腐蚀电流密度为4.828×10~(–5) A/cm~2,与镁合金基体相比,熔覆层的腐蚀电位值增加,腐蚀电流密度值变小,熔覆层的耐蚀性能得到提高。结论采用激光熔覆技术,能够在AZ91D镁合金基体表面制备Al-TiC涂层,由于硬质相AlTi_3(C,N)_(0.6),Al_3Mg_2,Mg_2Al_3,TiC等的存在,熔覆层的显微硬度和耐蚀性能显著提高。     

TiC增强钛基复合材料激光熔覆层显微组织及形成机理

在Ti-6A1-4V（质量分数，下同）合金表面进行了Ti＋TiC激光熔覆试验研究。利用SEM对熔覆层的显微组织进行了分析，提出了一个激光熔覆层显微组织演化过程模型，对显微组织的形貌特征和形成机理进行了解释。从复合材料的制备过程、质量、工艺性、制造成本和增强效果等多个方面，对激光熔覆Ti＋TiC复合粉末制备钛基复合材料的方法进行了分析。结果表明：采用激光熔覆Ti＋TiC复合粉末制备TiC／Ti复合材料是一种可行的方法。     

Selective Laser Melting of in-situ TiC/Ti5Si3 composites with novel reinforcement architecture and elevated performance

A novel Selective Laser Melting (SLM) process was applied to prepare bulk-form TiC/Ti₅Si₃ in-situ composites starting from Ti/SiC powder system. The influence of the applied laser energy density on densification, microstructure, and mechanical performance of SLM-processed composite parts was studied. It showed that the uniformly dispersed TiC reinforcing phase having a unique network distribution and a submicron-scale dendritic morphology was formed as a laser energy density of 0.4 kJ/m was properly settled. The 96.9% dense SLM-processed TiC/Ti₅Si₃ composites had a high microhardness of 980.3HV_0.2, showing more than a 3-fold increase upon that of the unreinforced Ti part. The dry sliding wear tests revealed that the TiC/Ti₅Si₃ composites possessed a considerably low friction coefficient of 0.2 and a reduced wear rate of 1.42 × 10^− 4 mm³/Nm. The scanning electron microscope (SEM) characterization of the worn surface morphology indicated that the high wear resistance was due to the formation of adherent and strain-hardened tribolayer. The densification rate, microhardness, and wear performance generally decreased at a higher laser energy density of 0.8 kJ/m, due to the formation of thermal cracks and the significant coarsening of TiC dendritic reinforcing phase.     

Effect of laser irradiation on failure mechanism of TiCp reinforced titanium composite coating produced by laser cladding

Laser cladding is an effective technique to coat a metallic substrate with a layer of a different nature. It has been widely reported that the most important combined parameters controlling the quality of the coating are the specific energy (E) and the powder density (Ψ). In the present work, clad deposits of Ti6Al4V + 60 wt.% TiC were prepared on a Ti6Al4V substrate using an optimum combination of E_c = 24 J/mm² and ψ_c = 3 mg/mm². These experiments were performed using a laser power of 400 and 600 W, in order to study the effect of laser power on the properties of the clad. The microstructure, phase composition and nanohardness of the coatings were investigated by optical microscopy, scanning electron microscopy and X-ray diffraction. During laser processing, TiC can be partially converted to TiC_X (X = 0.5) due mainly to the TiC dissolution into the laser-generated melting pool and subsequent precipitation during cooling. It was observed that the lower laser power limit reduces primary TiC dissolution but it also promotes secondary carbide alignment at the interface. On the other hand, the damage mechanism induced by high laser power is dominated by primary TiC particle cracking by the high stress concentration at the particle–matrix interface followed by ductile failure of the matrix. It is also remarkable that irradiance affects the TiC/TiC_x ratio despite E_c and ψ_c are fixed and it determines hardness distribution inside the coating.     

Effect of processing parameters on formability,microstructure, and micro-hardness of a novel laser additive manufactured Ti-6.38Al-3.87V-2.43Mo alloy

A novel Ti-6.38Al-3.87V-2.43Mo alloy was designed with a cluster formula of 12[Al-Ti12](V0.75Mo0.25Ti2)+4[Al-Ti12](Al3)by replacing Ti with Mo/V on the basis of the Ti-Al congruent alloy.The effects of laser power and scanning speed on the molten pool size,surface roughness,relative density,microstructure,and micro-hardness of single-track and bulk Ti-6.38Al-3.87V-2.43Mo samples prepared via laser additive manufacturing(LAM)were investigated.The results show that processing parameters significantly affect the formability,microstructure,and micro-hardness of the alloy.With decreasing laser power from 1,900 W to 1,000 W,the relative density is decreased from 99.86%to 90.91%due to the increase of lack-of-fusion;however,with increasing scanning speed,the relative density does not change significantly,but exceeds 99%.In particular,Ti-6.38Al-3.87V-2.43Mo samples of single-track and bulk exhibit a good formability under an input laser power of 1,900 W and a scanning speed of 8 mm·s_-1,and display the lowest surface roughness(Ra=13.33μm)and the highest relative density(99.86%).Besides,the microstructure of LAM Ti-6.38Al-3.87V-2.43Mo alloy coarsens with increasing laser power or decreasing scanning speed due to the greater input energy reducing the cooling rate.The coarsening of the microstructure decreases the microhardness of the alloy.     

激光熔覆CoCrFeNiTix高熵合金涂层的组织与性能

目的 研究Ti含量对激光熔覆CoCrFeNi高熵合金涂层的组织和性能的影响。方法 利用激光熔覆技术在45钢表面制备CoCrFeNiTi_x（x表示摩尔比值,x为0、0.2、0.4、0.6、0.8）高熵合金熔覆层,并通过Leica DVM6光学显微镜、扫描电镜（SEM）、X射线衍射仪（XRD）、显微硬度计、电化学工作站等设备,对单道和多道熔覆试样的宏观形貌、显微组织、显微硬度、耐腐蚀性能等方面进行分析研究。结果 随着Ti含量的增加,熔覆层的稀释率逐步增大,涂层与基材之间的冶金结合性能变好,但表面的成形质量变差;熔覆层随着Ti含量的增加,由单一的面心立方（FCC）相变为面心立方（FCC）和体心立方（BCC）相混合;在Ti含量的增加过程中,熔覆层的组织由树枝晶变为没有明显方向的等轴晶,且晶粒趋于细化;熔覆层的硬度随着添加元素Ti含量的增加而逐步提高,当x=0.8时硬度值提高至502.39HV0.3;随着Ti含量的增加,熔覆层的腐蚀电位逐渐先向正方向移动,后向负方向移动,腐蚀电流密度先减小后略有增加。结论 在CoCrFeNi合金体系中添加Ti元素,会导致熔覆层的成形质量恶化...     

Microstructure and synthesis mechanism of Al-Ti-C-Sr master alloy

Al-5Ti-0.5C-8Sr (mass fraction,%) master alloy was prepared using a melt reaction method.The microstructure and synthetic process of the master alloy were investigated by optical microscopy,X-ray diffraction,scanning electron microscopy and X-ray energy-dispersive spectrum.The results show that the master alloy is composed of α(Al),TiAl3,TiC,Al4Sr and Al-Ti-Sr phases.The synthesis mechanisms of the master alloy are as follows:TiAl3 is formed through the reaction between K2TiF6 and Al melt at 850 ℃;when the melt was heated up to 1 200?1 300 ℃,TiC was formed through the reaction:Ti+C(s)=TiC(s);Al4Sr was formed through the binary uniform reaction when Sr was added into the melt;after the following solidification process in the peritectic reaction:L(Al,Sr)+α(TiAl3)→β(Al-Ti-Sr),the enwrapped structure was formed with the outer layer of Al-Ti-Sr phase and the internal layer of TiAl3 phase.     

Microstructure and refinement performance of Al-Ti-C master alloy: Effect of excess Ti on the growth and nucleating ability of TiC particles

Al-5Ti-0.2C, Al-0.8Ti-0.2C, Al-8Ti-2C, and Al-10Ti master alloys were prepared and used to investigate the influence of excess Ti on the growth of TiC particles and its ability to nucleate Al-grains. The results of a microstructure analysis of TiC-containing alloys and refined CPAl were interrelated to the results of a refinement test. It was found that the presence of excess Ti is essential at the stage of master alloy preparation, as it facilitates the growth and uniform distribution of TiC within the structure. In Al-5Ti-0.2C alloy containing excess Ti, carbide particles grow faster and to a higher extent (from 0.29 μm to 0.44 μm) compared to Al-0.8Ti-0.2C alloy produced without excess Ti (from 0.29 μm to 0.32 μm). The results support the “Ti-transition zone theory” as the mechanism of grain refinement by TiC-containing master alloys. The refinement performance of Al-5Ti-0.2C is superior compared to the one achieved by adding Al-8Ti-2C and Al-10Ti master alloys in corresponding concentrations. For the TiC particles to become favourable nucleating sites, they must undergo certain interaction with excess Ti at the stage of master alloy preparation.     

7075铝合金表面激光熔覆Ti/TiBCN复合涂层的组织及性能

采用激光熔覆技术在7075铝合金表面制备了Ti/TiBCN复合涂层,研究了工艺参数对复合涂层的微观组织及性能的影响。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)研究了Ti/TiBCN复合涂层的相组成和微观组织;利用显微维氏硬度计和往复摩擦磨损试验机研究了Ti/TiBCN涂层的性能。结果表明:当激光功率1 000 W,扫描速度3 mm/s,送粉率300 mg/min时,Ti/TiBCN复合涂层质量最好。涂层上部由树枝晶和部分胞状晶组成,涂层中部为等轴晶,涂层下部呈现球形的TiBCN颗粒。与铝合金基体相比,涂层的平均硬度为519.4 HV0.2,是基体(~120 HV0.2)的4.3倍;涂层的平均摩擦因数为0.208,约是基体(0.442)的1/2;涂层磨损损失量为2.7 mg,约是基体(8.2 mg)的1/3。     

Wear Resistance Enhancement of Ti-6Al-4 V Alloy by Applying Zr-Modified Silicide Coatings

Zr-modified silicide coatings were prepared on Ti-6Al-4 V alloy by pack cementation process to enhance its wear resistance. The microstructure and wear properties of the substrate and the coatings were comparatively investigated using GCr15 and Al₂O₃ as the counterparts under different sliding loads. The obtained Zr-modified silicide coating had a multilayer structure, consisting of a thick (Ti,X)Si₂ (X represents Al, Zr and V elements) outer layer, a TiSi middle layer and a Ti₅Si₄ + Ti₅Si₃ inner layer. The micro-hardness of the coating was much higher than the substrate and displayed a decrease tendency from the coating surface to the interior. Sliding against either GCr15 or Al₂O₃ balls, the coatings showed superior anti-friction property to the Ti-6Al-4 V alloy, as confirmed by its much lower wear rate under each employed sliding condition.     

Influence of powder particle injection velocity on the microstructure of Al-12Si/SiCp coatings produced by laser cladding

The influence of powder particle injection velocity on the microstructure of coatings consisting of an Al-Si matrix reinforced with SiC particles prepared by laser cladding from mixtures of powders of Al-12 wt.% Si alloy and SiC was investigated both experimentally and by modeling. At low injection velocities SiC particles react with the molten aluminum alloy. Only a small fraction of SiC remains in the microstructure, which contains large amounts of particles of the reaction products Al₄SiC₄ and Si dispersed in the α-Al + Si eutectic matrix. By contrast, at high injection velocities chemical reactions between SiC and molten aluminum are almost entirely suppressed and the resulting microstructure consists only of SiC particles dispersed in the matrix. To investigate whether this behavior could be explained by the different temperatures reached by the injected particles as they fly through the laser beam, a physical-mathematical model describing the interaction between the laser beam and the powder stream in the off-axis blown powder laser cladding process was developed and applied to calculate the temperature attained by the powder particles as a result of their interaction with an Nd:YAG laser beam (λ = 1.06 µm). At an injection velocity of 1 m/s the maximum temperature attained by SiC and Al-12Si particles is 3150 and 180 ºC, respectively. This result demonstrates that particle injection velocity is a major parameter affecting the microstructure of coatings produced by laser cladding, and must be carefully controlled.     

SiCf/Ti-22Al-23Nb-2Ta合金复合材料的界面微结构

利用分析电子显微镜（AEM）研究了磁控溅射法＋真空热压方法制备的SiC纤维增强Ti-22Al—23Nb-2Ta（原子分数，％）合金复合材料的界面微结构．该复合材料的纤维／合金界面由细晶粒的TiC＋TiSi层、等轴晶TiC层和（Al，Ti）Nb2相层组成．界面的形成主要是基体合金中的Ti元素与SiC纤维表面的C涂层直接反应生成TiC；同时导致在次层形成贫Ti层和贫Ti层中Nb元素富集，以致形成（Al，Ti）Nb2相．     

Microstructure and properties of TiB/Ti-6Al-4V coatings produced with laser treatments

TiB/Ti-6Al-4V metal-matrix composite (MMC) layers were produced on Ti-6Al-4V substrates by laser cladding. A TiB₂/Ti powder mixture was used as a precursor to obtain a dispersion of TiB needles in the Ti alloy matrix, with the aid of an exothermic reaction between TiB₂ and Ti. A eutectic microstructure was obtained that consisted of an extremely homogeneous dispersion of TiB eutectic needles in the Ti alloy matrix, having a volume fraction as high as 0.33. Also, an equilibrium-like microstructure was found, consisting of a dispersion of both primary and eutectic TiB needles inside the Ti alloy matrix. An analysis of the geometry of the layers was performed and proved successful in determining the percentage of B. Further, it correctly predicted the variation of atomic B content as a function of laser power. The relative wear resistance coefficient, defined as the wear coefficient of the uncoated matrix divided by that of coating, shows an improvement by a factor as high as 1500 for the eutectic microstructure. This paper was presented at the 2nd International Surface Engineering Congress sponsored by ASM International, on September 15–17, 2003, in Indianapolis, Indiana, and appeared on pp. 411–18 of the Proceedings.     

AA6063铝合金表面激光熔覆TiC/Al_3 Ti复合材料涂层

将Al、Ti和TiC 粉末预涂在AA6063铝合金表面,采用激光熔覆法制备了TiC/Al_3Ti复合材料涂层,分析了激光熔覆层的显微组织和硬度分布.结果表明,采用合适的激光工艺可获得无裂纹和孔洞且表面平整的熔覆层.熔覆层由枝晶状Al_3Ti、枝晶间α-Al和均匀分布的TiC颗粒组成,TiC颗粒在激光辐照过程中未发生熔解,熔覆层与基材的界面结合良好.随与熔覆层表面距离的增加,Al_3Ti枝晶的尺寸变大,α-Al的含量减少.激光熔覆层的硬度可达700 HV0.2,显著改善了AA6063铝合金的表面硬度.     

Microstructure and properties of laser cladded B4C/TiC/Ni-based composite coating

In order to study the effect of TiC/B₄C ceramic particles on the microstructure evolution and microhardness of Ni204-based cladding coating, TiC/B₄C/Ni204-based composite coatings were fabricated by laser cladding. The results showed that the TiC ceramic particles in the 30%TiC+70%Ni204 coating do not decompose. TiC is the main reinforcing phase in the coating; however, in 30%B₄C + 5%TiC+65%Ni204 composite coating, TiB₂ phase was in situ synthesized, and graphite, Fe₂B, Ti-Mo-Nb, (Ti, Nb, Mo)(B, C) were formed simultaneously in the coating. The addition of TiC promoted the dissolution and reaction of B₄C. In the presence of 30%TiC, the average microhardness and friction coefficient of the coating were 966.4 HV_0.5 and 0.198, respectively, which were 3.23 and 0.281 times of the initial Ni204 coating. In the presence of 30%B₄C and 5%TiC, the average microhardness and friction coefficient of the coatings were 1308.2HV_0.5 and 0.530, respectively, which were 4.38 and 0.752 times of the initial coatings. The enrichment of TiC is proportional to the hardness of the coating.     

激光功率对超声辅助激光熔覆Al2O3-ZrO2陶瓷力学性能的影响

采用激光熔覆工艺在Ti-6Al-4V合金基体上制备Al₂O₃-ZrO₂陶瓷层,探讨在超声辅助下不同激光功率对熔覆层形貌及性能的影响。通过金相显微镜,X射线衍射,扫描电镜,显微硬度测试仪及摩擦磨损试验机研究了熔覆层的宏观形貌,截面形貌,物相组成,微观结构,显微硬度和磨损行为。结果表明:随着激光功率的增加,熔覆层稀释率先增加后降低,激光功率从1100 W增加到1500 W时,稀释率分别为65.86%、68.55%、76.04%、71.57%和68.23%;熔覆层主要由TiAl、TiO和ZrO₂组成;随着激光功率的增加,熔覆层显微硬度呈现先增加后减小的趋势;与其他3种熔覆层(激光功率为1300、1400和1500 W)相比,激光功率为1200 W的熔覆层平均摩擦因数相对较低,约为0.27,该熔覆层的磨损机理为磨粒磨损,其他3种熔覆层的磨损机理为磨粒磨损和粘着磨损。     

钛基复合材料激光熔覆层显微组织及其强化机制

利用激光熔覆技术在Ti-6A1-4V合金表面制备了TiC增强钛基复合材料涂层，复合材料的硬度明显高于基体，平均硬度可达940HV0.2。对复合材料的显微组织分析表明：TiC增强钛基复合材料的强化机制以细晶强化和弥散强化为主。     

Effect of Zr addition on microstructures and mechanical properties of Ni-46Ti-4Al alloy

The microstructures and mechanical properties of Ni-(46-x)Ti-4Al-xZr (x = 0-8, at.%) alloys have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and mechanical tests. The results show that the Ni-Ti-Al-Zr alloys are composed of TiNi and (Ti, Al) 2 Ni with Zr as a solid solution element in both phases, and the third phase, (Zr, Ti, Al) 2 Ni, appears in Ni-40Ti-4Al-6Zr and Ni-38Ti-4Al-8Zr alloys. The compressive yield strength at room temperature increases with the increase of Zr content due to the solid-solution strengthening of Zr and precipitation strengthening of (Ti, Al, Zr) 2 Ni phase. However, the Ni-42Ti-4Al-4Zr alloy exhibits the maximum compressive yield strength at 873 and 973 K because of the softening of (Zr, Ti, Al) 2 Ni phase in the alloys with more Zr addition. The tensile stress-strain tests and the SEM fracture surface observations show that the brittle to ductile transition temperature of Ni-42Ti-4Al-4Zr alloy is between 873 and 923 K.