铸铁表面原位合成TiC/Al3Ti复合材料

对Al-Ti-C体系进行热力学分析,在氩气保护下进行热爆反应试验.采用铸造反应合成技术在铸铁表面原位合成TiC/Al3Ti复合材料.研究热爆产物及表面复合材料的物相、组织和界面形貌,并对其形成机理进行探讨.结果表明:采用热爆工艺使Al-Ti-C体系发生反应,生成纯净的TiC/Al3Ti复合产物.在熔融铁液作用下,Al-Ti-C体系反应完全,制备出纯净的TiC颗粒增强金属间化合物基表面复合材料.表面复合材料组织致密,与铁基体界面为良好的冶金结合.当TiC含量较少时,颗粒呈条状;随着TiC含量的提高,颗粒尺寸逐渐减小,由长条状向粒状及细粒状转化.     

Feasible process for producing in situ Al/TiC composites by combustion reaction in an Al melt

In situ Al/TiC composites with a homogeneous distribution of TiC reinforcements were prepared by adding a reactant mixture of Al-Ti-C to an Al melt. A certain amount of CuO addition facilitates a combustion reaction of the Al-Ti-C system and thereby enables the formation of in situ TiC at a reasonably low temperature range of 750–920 °C. Synthesised TiC particles with sizes of 1–2 μm are present in the Al matrix along with Al₃Ti. Besides the CuO addition, the melt temperature plays a significant role in the final microstructure of the composites. Increase in the melt temperature up to 920 °C with CuO provides more external heat input and initiates the combustion reaction within a few seconds. Pellet microstructure evidently shows that the polygonal Al₃Ti originates from the unreacted layer of which the distance is significantly shortens by increasing the melt temperature. The suppression of the Al₃Ti formation is the most likely to occur at 920 °C, with producing a large volume fraction of TiC in situ synthesised.     

Research on Crack-Filling Heat Treatment and Hydrogen Permeation Test of Self-healing Tritium Permeation Barriers

A TiC + mixture (TiC/Al₂O₃ (1:1 wt.%)) +Al₂O₃ self-healing triple layer coating (TLC) was designed and manufactured by our group, and the crack-filling heat treatment process had been roughly explored in the past. In this work, the accelerating test with a thick TiC + mixture (TiC/Al₂O₃ (1:1 wt.%)) double-layer coating (DLC) was carried out. The DLC coating warped when the heat treatment temperature was lower than 550 °C, which was rare in similar researches, and it crushed into fan-shaped pieces when the treatment temperature was higher than 650 °C. The two different spalling failures were explained by weight gain, porosity and stress analyses. The heating rate had a significant effect. The bonding strength and hydrogen permeation of the TLC samples were also tested. Remaining at 650 °C for 40 h was proved to be an optimal crack-filling heat treatment process, considering the hydrogen resistance.     

Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiC Composite Prepared by Spark Plasma Sintering Process: Evaluation of Mechanical and Tribological Properties

Al₂O₃-10TiC composites were synthesized by spark plasma sintering (SPS) process. Microstructural and mechanical properties of the composite reveal homogeneous distribution of the fine TiC particles in the matrix. The samples were produced with different sintering temperature, and it shows that the hardness and density gradually increases with increasing sintering temperature. Abrasion wear test result reveals that the composite sintered at 1500 °C shows high abrasion resistance (wt. loss ~ 0.016 g) and the lowest abrasion resistance was observed for the composite sample sintered at 1100 °C (wt. loss ~ 1.459 g). The profilometry surface roughness study shows that sample sintered at 1100 °C shows maximum roughness (R_a = 6.53 µm) compared to the sample sintered at 1500 °C (R_a = 0.66 µm) corroborating the abrasion wear test results.     

TiC/Ti复合材料激光熔覆层的冲击磨粒磨损性能

在Ti6A14V表达通过激光熔覆工艺原位合成TiC/Ti金属基复合材料涂层，其基体组织结构随表层预置合金粉末成分的变化而改变，采用单摆划痕装置测试原位合成TiC/Ti复合材料涂层的冲击磨粒磨损性能，结果表明，与基材Ti6A14V相比复合材料激光熔覆层的抗冲击磨粒磨损性能提高了2倍，且随表层预置粉末中Cr3C2含量的增加，反应生成的TiC含量增加，涂层抗冲击磨料磨损性能提高。     

Influence of FeCrAl Content on Microstructure and Bonding Strength of Plasma-Sprayed FeCrAl/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Coatings

Low-power plasma-sprayed FeCrAl/Al₂O₃ composite coatings with 1.5 mm thickness have been fabricated for radar absorption applications. The effects of FeCrAl content on the coating properties were studied. The FeCrAl presents in the form of a few thin lamellae and numerous particles, demonstrating relatively even distribution in all the coatings. Results show that the micro-hardness and porosity decrease with the increase in FeCrAl content. With FeCrAl content increasing from 28 to 47 wt.%, the bonding strength of the coatings with 1.5 mm thickness increases from 10.5 to 27 MPa, and the failure modes are composed of cohesive and adhesive failure, which are ascribed to the coating microstructure and the residual stress, respectively.     

Grain refinement of AZ31 magnesium alloy by new Al-Ti-C master alloys

New Al₄C₃-containing Al-Ti-C master alloys (Al-0.6Ti-1C and Al-1Ti-1C) were developed by introducing Ti element into Al-C melt using melt reaction method, in which most of the TiC particles distribute around Al₄C₃ particles. It is believed that most of the C firstly reacts with Al melt and form Al₄C₃ particles by the reaction Al(l)+C(s)→Al₄C₃(s), and after adding Ti into the Al-C melt, the size of Al₄C₃ particles is decreased and the distribution of Al₄C₃ is improved through the reaction Ti(solute)+Al₄C₃(s)→TiC(s)+Al(l). With the addition of 1% Al-1Ti-1C master alloy, the average grain size of AZ31 is reduced sharply from 850 μm to 200 μm, and the grain morphology of α-Mg transits from a fully-developed equiaxed dendritic structure to a petal-like shape. Al-C-O-Mn-Fe compounds are proposed to be potent nucleating substrates for primary Mg. Appropriate addition of Ti is believed to increase the grain refinement efficiency of Al₄C₃-containing Al-Ti-C master alloys in AZ31 alloy.     

Development of a Novel Cast 6351 Al-Al4SiC4 In Situ Composite

In this research work 6351 Al-Al₄SiC₄ composite has been developed through stir casting route with incorporation of fine TiC powder in 6351 Al melt. During stir casting, round shaped Al₄SiC₄ particles were generated as TiC reacted with molten aluminum. These Al₄SiC₄ particles were found to be acting as nucleation sites for primary α (causing grain refinement) along with engulfment effects promoting particle distribution without clustering. Furthermore, as the volume fraction of Al₄SiC₄ particles increased, the proportion of dendritic region decreased (more equiaxed grains appeared) and the overall grain size of the matrix decreased. This resulted in an improved strength and ductility of the composite. Equations were developed with a reasonable accuracy correlating the strength with microstructural parameters. An excellent combination of strength (UTS = 215 MPa) and ductility (%Elongation = 10) was obtained for 6351 Al-7 vol.% Al₄SiC₄ composite as compared to base cast 6351 Al alloy (UTS = 121 MPa, %Elongation = 3).     

Effects of Plasma-spraying Powers on Microstructure and Microhardness of In-Situ Nanostructured FeAl2O4 Composite Coatings

In-situ nanostructured FeAl₂O₄ composite coatings were prepared using plasma spraying of Al/Fe₂O₃ composite powders applying different spraying powers. The effects of plasma-spraying powers on microstructure and property of FeAl₂O₄ composite coatings were investigated. The results indicated the composite coatings had the microstructure with thin lamellar splats rich in FeAl₂O₄ as matrix, and dispersed granules rich in Fe and thin lamellar splats rich in Al₂O₃ as second phases. The reaction degree of Al/Fe₂O₃ composite powders increased while applying spraying power of 25-30 kW and then decreased while applying spraying power of 30-40 kW, which first resulted in the increase and then in the decrease of the Al₂O₃ content. The coating prepared by applying spraying power of 30 kW had the maximum microhardness, which was attributed to the maximum Al₂O₃ content present in the coating and the most uniform microstructure of the coating.     

钛合金表面氩弧熔覆TiC增强复合涂层组织与性能分析

把石墨粉末预涂在钛合金表面上,利用氩弧熔覆技术成功制备出原位自生TiC增强的金属基复合涂层。利用扫描电镜、X射线衍射仪和能谱仪分析了熔覆涂层的显微组织,探讨了增强相TiC的生成机制;利用显微硬度仪测试了复合涂层的显微硬度并用磨损试验机考察了其在室温干滑动磨损条件下的耐磨性能。结果表明,氩弧熔覆涂层组织均匀致密,原位自生TiC呈树枝晶和细碎的条状均匀地分布于整个涂层中;由TiC增强的复合涂层明显地改善了钛合金的表面硬度．平均硬度约为700HV0．2且沿层深方向呈梯度分布;涂层在室温干滑动磨损条件下的耐磨性明显优于基体,约为钛合金的10．5倍．     

Tribological Behavior of Plasma-Sprayed Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-20 wt.%TiO<Subscript>2</Subscript> Coating

Al₂O₃-20 wt.% TiO₂ ceramic coatings were deposited on the surface of Grade D steel by plasma spraying of commercially available powders. The phases and the microstructures of the coatings were investigated by x-ray diffraction and scanning electron microscopy, respectively. The Al₂O₃-20 wt.% TiO₂ composite coating exhibited a typical inter-lamellar structure consisting of the γ-Al₂O₃ and the Al₂TiO₅ phases. The dry sliding wear behavior of the coating was examined at 20 °C using a ball-on-disk wear tester. The plasma-sprayed coating showed a low wear rate (~4.5 × 10^?6 mm³ N^?1 m^?1), which was <2% of that of the matrix (~283.3 × 10^?6 mm³ N^?1 m^?1), under a load of 15 N. In addition, the tribological behavior of the plasma-sprayed coating was analyzed by examining the microstructure after the wear tests. It was found that delamination of the Al₂TiO₅ phase was the main cause of the wear during the sliding wear tests. A suitable model was used to simulate the wear mechanism of the coating.     

Effect of si addition on mechanical alloying behavior and creep properties of Al-10Ti-xSi alloys

Al-10Ti-xSi alloys (x=0∼6wt.%) have been mechanically alloyed under Ar atmosphere using an attritor and the alloying process has been investigated. From Al-10Ti composite powders, supersaturated Al(Ti) powders were obtained after mechanical alloying. In the ternary mixture, fine Si particles were observed to be distributed in the Al(Ti) matrix due to both the negligible solid solubility of Si in the Al matrix and the weaker chemical interaction of Si with Al, as compared with Ti. The sealed compacts were hot extruded to full density at 450°C with an extrusion ratio of 12:1. The microstructures and creep properties of the hot extruded alloys were examined. During consolidation, Si particles were dissolved in Al₃Ti up to 4 wt.% Si to form the (Al(Si))₃Ti phase, and the Ti₇Al₅Si₁₂ phase was formed beyond the solubility limit of Si in Al₃Ti. The transition from the Coble creep mechanism at low stresses and temperatures to dislocation one at high stresses and temperatures was observed. The stress and temperature of the transition from diffusional to dislocation creep became higher as Si concentration increased. This was due to an enhancement of Al₃Ti particle strength with increasing Si content as a result of Si incorporation. Thus, the addition of Si enhances the creep resistance of the MA Al-10Ti alloy.     

Comparison of 10 μm and 20 nm Al-Al2O3 Metal Matrix Composite Coatings Fabricated by Low-Pressure Cold Gas Dynamic Spraying

Cold-gas dynamic spraying (“cold spraying”) was used to deposit aluminum-alumina (Al-Al₂O₃) metal-matrix composite (MMC) coatings onto 6061 Al alloy. The powders consisted of ?45 μm commercially pure Al that was admixed with either 10 μm or agglomerated 20 nm Al₂O₃ in weight fractions of 25, 50, 75, 90, and 95 wt.%. Scanning electron microscopy (SEM), Vickers microhardness testing, and image analysis were conducted to determine the microstructure, properties, and the volume fractions of reinforcing particles in the coatings, which was then converted to weight fractions. As the weight fraction of the Al₂O₃ in the coatings increased, the hardness values of the MMC coatings increased. A maximum hardness of 96 ± 10 HV_0.2 was observed for the MMC coating that contained the agglomerated 20 nm Al₂O₃ particles, while a maximum hardness of 85 ± 24 HV_0.2 was observed for the coatings with the 10 μm Al₂O₃ particles. The slight increase in hardness of the coating containing the agglomerated 20 nm Al₂O₃ particles occurred in a coating of Al₂O₃ content that was lower than that in the coating that contained the 10 μm reinforcing Al₂O₃ particles. The increased hardness of the MMC coatings that contained the agglomerated 20 nm Al₂O₃ particles and at lower reinforcing particle content was attributed to the increased spreading of the nanoagglomerated particles in the coating, which increased load-sharing and reinforcement capability of the particles. These results suggest that the use of nanoagglomerated, reinforcing hard-phase particles in cold-sprayed MMC coatings may be a more efficient alternative to the use of conventional micronsized reinforcing particles.     

铝合金表面激光熔覆原位自生TiC增强金属基复合材料涂层

以Ti,SiC混合粉末作为预置合金涂层,采用2kW连续Nd:YAG固体激光器进行激光熔覆处理,在6061铝合金表面借助于接触反应法制备原位生成TiC颗粒增强Al-Ti复合材料涂层。试验结果表明：采用适合的激光辐照工艺参数,可获得增强相TiC弥散分布,以Ti-Al金属间化合物及Al过饱和固溶体为主要组成相的复合材料熔覆层组织。TiC颗粒与复合材料基体润湿良好,熔覆层结晶致密,与6061铝合金基材呈良好的冶金,珂明显地改善铝合金的表面性能。     

Sliding Wear Behavior of TiC-Reinforced Cu-4 wt.% Ni Matrix Composites

The present investigation explores the effect of TiC content on the sliding wear properties of Cu-4 wt.% Ni matrix composites. Cu-4 wt.% Ni ? x wt.% TiC (x = 0, 2, 4 and 8 wt.%) metal matrix composites were developed by powder metallurgy route. Their friction and wear was studied under dry sliding at different loads of 5, 7.5 and 10 N and constant sliding speed of 2 m/s using a pin-on-disk machine. The metallographic observations showed an almost uniform distribution of TiC particles in the matrix. Hardness of the composites increased with increasing TiC content (up to 4 wt.%). Friction and wear results of TiC-reinforced composites show better wear resistance than unreinforced matrix alloy. However, the optimum wear resistance was observed for 4 wt.% TiC-reinforced composites. Worn surfaces of specimens indicated the abrasion as the primary mechanism of wear in all the materials investigated in the study. The observed behavior has been explained on the basis of (1) the hardness which results in a decrease in real area of contact in composites containing TiC particles and (2) the formation of a transfer layer of wear debris on the surface of the composites which protects underlying substrate by inhibiting metal-metal contact.     

Correlation of microstructure with high-temperature hardness of (TiC,TiN)/Ti–6Al–4V surface composites fabricated by high-energy electron-beam irradiation

Correlation of microstructure with high-temperature hardness of (TiC,TiN)/Ti–6Al–4V surface composites fabricated by high-energy electron-beam irradiation was investigated in this study. TiC, TiN and TiC+TiN powder mixtures containing 50% CaF₂ flux were deposited on the surface of a Ti–6Al–4V alloy substrate, and irradiated by high-energy electron beam to form 1-mm-thick, defect-free surface composite layers. The surface composite layers contained a large amount (over 30 vol.%) of precipitates such as TiC, TiN, (Ti_xAl_1−x)N and Ti(C_xN_1−x) in the martensitic or N-rich acicular α-Ti matrix. This microstructural modification including the formation of hard precipitates and hardened matrices in the surface composite layers improved hardness and high-temperature hardness two to four times greater than that of the substrate. In particular, the surface composite fabricated with TiN powders had the highest hardness because of the highest volume fraction of TiN and (Ti_xAl_1−x)N distributed in the hardened N-rich acicular α-Ti matrix. These findings suggest that the (TiC,TiN)/Ti–6Al–4V surface composites can be used for structural materials requiring excellent thermal resistance.     

The Effect of Ti on Microstructural Characteristics and Reaction Mechanism in Bonding of Al-Ceramic Composite

The effect of Ti on microstructural characteristics and reaction mechanism in bonding of Al-Ceramic composite was studied. Ti and Al-Ceramic composite were diffusion welded at 550, 600, 700, 800, and 900 °C in a vacuum furnace. The microstructures and compositions of the interface layers were analyzed, and the mechanical properties and fracture morphology of the joints were examined. The results indicated that there was a systematic switch from Ti/Ti₇Al₅Si₁₂/composite at 600 °C and Ti/TiAl₃/Ti₇Al₅Si₁₂/composite at 700 °C to Ti/Ti₇Al₅Si₁₂/TiAl₃/Ti₇Al₅Si₁₂/composite at 800 °C and Ti/Ti₇Al₅Si₁₂/TiAl₃/composite at 900 °C. The formation of TiAl₃ at 700 and 800 °C depended on Al segregation, which was an uphill diffusion driven by chemical potential. The maximum shear strength was 40.9 MPa, found in the joint welded at 700 °C. Most joints fractured between Ti₇Al₅Si₁₂ and Al-Ceramic composite. In any case, Ti₇Al₅Si₁₂ was favorable for Al-Ceramic composite welding, which attached to Al-Ceramic composite, reducing the differences in physiochemical properties between SiC and metal, improving the mechanical properties of the joints and increasing the surface wettability of Al-Ceramic composite.     

In-situ production and microstructures of iron aluminide/TiC composites

In this study we have tried to produce the titanium carbide reinforced iron aluminide composites by in-situ reaction between titanium and carbon in liquid iron–aluminum alloy doped with titanium and carbon. A homogeneous distribution of titanium carbide particles in the iron aluminide matrix up to about 16 vol% of titanium carbide was intended without agglomeration. The composition of TiC formed during in-situ reaction was investigated by ICP analysis and the Combustion-Infrared Absorption method after chemical dissolution of the iron aluminide matrix. It is found that the composition of titanium carbide formed during melt processing is an average of Ti–48.4 mol% C. In addition, titanium carbide has very low solubility of Fe and Al. The microstructure of composites consists of three different regions; primary large TiC particles of 5–40 μm, matrix with small dendritic TiC particles of about 1 μm and particle-free regions around primary large TiC particles. The formation of this complex microstructure can be explained by assuming the Fe₃Al–TiC pseudo-binary system containing the eutectic reaction. Particle-free regions are halos of iron aluminide phase and the formation of halos is explained by coupled zone concept. Subsequent heat treatment at 1373 K for 48 h induces spheroidization and/or coarsening of small TiC particles, while microstructure after heat treatment at 973 K for 48 h exhibits the additional formation of small TiC precipitates. Though excess 1 mol% Ti addition over the Ti content for TiC formation is soluble to Fe–28 mol% Al, excess 1 mol% C addition forms the secondary Fe₃AlC phase during melt processing.     

Tribocorrosion Behavior of Fe-Based Amorphous Composite Coating Reinforced by Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in 3.5% NaCl Solution

Although corrosion and friction/wear behavior of Fe-based amorphous coatings and their composites has been extensively studied during the past decade, there is very limited work related to tribocorrosion behavior. In this paper, the tribocorrosion behavior of a Fe-based amorphous composite coating reinforced with 20 wt.% Al₂O₃ particles was investigated in a 3.5% NaCl solution on a ball-on-disk tester and was compared to the monolithic amorphous coating and 316L stainless steel (SS). The results showed that the amorphous composite coating exhibited the highest tribocorrosion resistance among the three materials tested, as evidenced by the lowest coefficient of friction (~0.3) and tribocorrosion wear rate (~1.2 × 10^?5 mm³/N·m). In addition, potentiodynamic polarization measurements before and during tribocorrosion testing demonstrated that corrosion resistance of the amorphous composite coating was not influenced so much by mechanical loading compared to the amorphous coating and the 316L SS. Observations on the worn surface revealed a corrosion-wear- and oxidational-wear-dominated tribocorrosion mechanism for the composite coatings. The excellent tribocorrosion resistance of the composite coating results from the effect of chemically stable Al₂O₃ phase which resists oxidation and delamination during sliding, along with poor wettability with corrosive NaCl droplets.     

The Effect of Post-grinding Heat Treatment of Alumina and Ag-Cu-Ti Braze Preform Thickness on the Microstructure and Mechanical Properties of Alumina-to-Alumina-Brazed Joints

Alumina-to-alumina-brazed joints were formed using 96.0 and 99.7 wt.% Al₂O₃ and TICUSIL^® (68.8Ag-26.7Cu-4.5Ti wt.%) preforms of different thicknesses. Brazing was conducted in a vacuum of 1 × 10^?5 mbar at 850 °C for 10 minutes. Joint strengths were evaluated using four-point bend testing and were compared to flexural strengths of standard test bars. Post-grinding heat treatment, performed at 1550 °C for 1 hour, did not affect the average surface roughness or grain size of either grades of alumina but affected their average flexural strengths with a small increase for 96.0 wt.% Al₂O₃ and a small decrease for 99.7 wt.% Al₂O₃. As the TICUSIL^® preform thickness was increased from 50 to 100 µm, the average strengths of both 96.0 and 99.7 wt.% Al₂O₃ brazed joints improved. Joints made using 100-µm-thick TICUSIL^® preforms predominantly consisted of Cu-Ti phases which formed due to excess Ti in the interlayers and non-uniform Ag-rich outflow. Brazed joints of 96.0 wt.% Al₂O₃ made using 100-µm-thick TICUSIL^® preforms achieved an average joint strength of 238 MPa with consistent failure in the ceramic.