Synthesis and characterisation of free standing,one­dimensional,Al–SiC based functionally gradient material

Abstract

In the present study, an aluminium–silicon carbide based functionally gradient material was successfully synthesised using a new technique termed here as gradient slurry disintegration and deposition process. The gradient of SiC was successfully established using this technique for 21 wt-%SiC. The results were confirmed using microstructural characterisation techniques, microhardness measurements, and wear rate determination. The results further revealed that an increase in the weight percentage of silicon carbide particulates along the deposition direction lead to a concurrent increase in porosity, degree of clustering, and microhardness while the nature of silicon carbide/aluminium interfacial integrity remained the same. The results of wear rate determination indicated that a difference of ～9.53 vol.-%SiC on the opposite faces of the functionally gradient material led to the wear resistance increasing to ～31.5× that of the high aluminium end. An attempt is made to interrelate the processing methodology, microstructure, microhardness, and wear rate results obtained in the present study.     

Synthesis of Al/SiC based functionally gradient materials using technique of gradient slurry disintegration and deposition: effect of stirring speed

Abstract

In the present study, Al/SiC based functionally gradient materials (FGMs) were successfully synthesised using the gradient slurry disintegration and deposition technique. Gradients of SiC for the starting weight of 18% were successfully established by varying the stirring speed of the molten melt. The results revealed, in general, increases in the weight percentage and clustering tendency of SiC, porosity, and microhardness and a reduction in grain size, with increasing distance from the base of the FGM ingots. The results also showed that an increase in the stirring speed increases the homogeneity of SiC particulates distribution, thus resulting in a decrease in the gradient of reinforcement along the deposition direction. Furthermore, an increase in the stirring speed decreases the number of clusters formed per unit area. An attempt has been made in the present work to establish the trend between processing parameters, such as stirring speed and the gradient of SiC particulates realised in the ingots.     

In‐situ composite coating on powder metallurgy master alloy fabricated by vacuum hot‐pressing sintering technology

A material consisting of an in‐situ titanium carbide reinforced nickel‐aluminide (Ni₃Al) coating and a powder metallurgy master alloy was fabricated by vacuum hot‐pressing sintering technology. A metallurgical bonded, pores‐free interface between composite coating and powder metallurgy master alloy was formed at the sintering temperature of 1050 °C, pressure of 10^‐4 Pa and pressing pressure of 40 MPa. The phase, microstructure and wear behavior of composite coating were investigated. The results showed that polygonal titanium carbide particulates with various sizes were homogeneously distributed in nickel‐aluminide matrix. The sintering temperature, pressing pressure and heat from as‐reactions‐formed coating green compact facilitated the pore infiltration with transiently generated liquid phases and ensured the high‐intensity metallurgical bonding between composite coating and powder metallurgy master alloy. Due to the abnormal elevated‐temperature properties of nickel‐aluminide matrix, titanium carbide particulates reinforcement and the mechanically mixed layer protection, TiC/Ni₃Al‐coated parts demonstrated superior wear resistance and lower friction coefficient while compared with Ni₃Al‐coated parts and H13 steel.     

Particle effects on friction and wear of aluminium matrix composites

Particle effects on friction and wear of 6061 aluminium (6061 Al) reinforced with silicon carbide (SiC) and alumina (Al₂O₃) particles were investigated by means of Vickers microhardness measurements and scratch tests. Unreinforced 6061 Al matrix alloy was also studied for comparison. To explore the effect of heat treatment, materials subjected to three different heat treatment conditions, i.e. under-aged, over-aged and T6, were used. Multiplescratch tests using a diamond and a steel indentor were also carried out to simulate real abrasive wear processes. Vickers microhardness measurements indicated that T6 heattreated composites had the highest hardness. Single-scratch tests showed that the variation of friction coefficient was similar to that of Vickers hardness and the peak-aged composites exhibited the best wear resistance. The wear rate of fine particle-reinforced composites was mainly affected by hardness. However, the wear rate of large particle-reinforced composites was influenced by both the hardness and fracture of the particles.     

Impact of graphite particle on milling of Al/15Al2O3 and Al/15Al2O3/5Gr composites

ABSTRACT

Hybrid Metal Matrix Composites (MMCs) are a new class of composites, formed by a combination of the metal matrix and more than one type of reinforcement having different properties. Machining of MMCs is a difficult task because of its heterogeneity and abrasive nature of reinforcement, which results in excessive tool wear and inferior surface finish. This paper investigates experimentally the addition of graphite (Gr) on cutting force, surface roughness and tool wear while milling Al/15Al₂O₃ and Al/15Al₂O₃/5Gr composites at different cutting conditions using tungsten carbide (WC) and polycrystalline diamond (PCD) insert. The result reveals that feed has a major contribution on cutting force and tool wear, whereas the machined surface roughness was found to be more sensitive to speed for both composite materials. The incorporation of graphite reduces the coefficient of friction between the tool–workpiece interfaces, thereby reducing the cutting force and tool wear for hybrid composites. The surface morphology and worn tool are analyzed using scanning electron microscope (SEM). The surface damage due to machining extends up to 200 µm for Al/15Al₂O₃/5Gr composites, which is beyond 250 µm for Al/15Al₂O₃ composites.     

In situ fabrication of titanium carbide particulates-reinforced iron matrix composites

Titanium carbide (TiC) particulates-reinforced iron matrix composites were prepared by in situ fabrication method combining an infiltration casting with a subsequent heat treatment. The effects of different heat treatment times (0, 1, 6 and 11 h) at 1138 °C on the phase evolution, microstructural features, and properties of the composites were investigated. The as-prepared composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and microhardness and wear resistance tests. The XRD results showed that the composites consisted of graphite, α-iron and titanium carbide after heat treatment at 1138 °C for 11 h. The SEM observation revealed that the formed TiC particulates were homogenously distributed in the iron matrix. The average microhardness of the composite heat treated at 1138 °C for 6 h increased depending upon the region: 209 HV_0.1 (iron matrix) < 787 HV_0.1 (titanium wire) < 2667 HV_0.1 (composite region). After being heat treated at 1138 °C for 11 h, the composite indicated no considerable change in microhardness value, and the average microhardness of the composite region was about 2354 HV_0.1. The highest microhardness value obtained for the composite region was due to the formation of titanium carbide particulates as reinforcement phase within the iron matrix. Relative wear resistance was determined by a pin-on-disc wear test technique under different loads, and as a result, the composites containing higher volume fraction of hard titanium carbide particulates presented higher wear resistance compared with the unreinforced gray cast iron.     

Effect of metal coating of reinforcements on the microstructure and mechanical properties of Al-Al2O3 nanocomposites

The effects of various methods of reinforcement modification on the microstructure and mechanical properties of Al–Al₂O₃ nanocomposites were investigated. Alumina nanoparticles were modified by electroless deposition of Cu, Ni and Co. Subsequently, aluminium matrix nanocomposites reinforced with uncoated and coated nanoparticles were produced by the stir casting method. The results of microstructural analysis showed improved wettability of coated nanoparticles in the molten aluminium alloy. Furthermore, coated nanoparticles exhibited a more desirable interface with the matrix and were homogenously distributed within it. The mechanical properties of the nanocomposites were improving significantly when coated nanoparticles were used as reinforcements. Among the reinforcement modification methods, Ni-coating was recognised as being more effective for improving the mechanical properties of Al–Al₂O₃ nanocomposites.     

Relationship between thermal and sliding wear behavior of Al6061/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> metal matrix composites

Al6061 alloy and Al6061/Al₂O₃ metal matrix composites (MMCs) were fabricated by stir casting. The MMCs were prepared by addition of 5, 10 and 15 wt% Al₂O₃ particulates and the size of particulates was taken as 16 μm. The effect of Al₂O₃ particulate content, thermal properties and stir casting parameters on the dry sliding wear resistance of MMCs were investigated under 50–350 N loads. The dry sliding wear tests were performed to investigate the wear behavior of MMCs against a steel counterface (DIN 5401) in a block-on-ring apparatus. The wear tests were carried out in an incremental manner, i.e., 300 m per increment and 3,000 m in total. It was observed that, the increase in Al₂O₃ vol% decreased both thermal conductivity and friction coefficient and hence increased the transition load and transition temperature for mild to severe wear during dry sliding wear test.     

Friction and wear of P/M Al-20Si-Al2O3 composites in kerosene

The results of friction and wear of powder metallurgy (P/M) Al-20 wt% Si-3 wt% Cu-1 wt% Mg-(2.5–10) vol% Al₂O₃ particulate-reinforced composites have been compared with those of the P/M aluminium alloy matrix and A-390 cast piston aluminium alloy. It was found that Al₂O₃ reinforcement reduces wear by five to eight times when mating with cast iron in kerosene: The higher the reinforcement volume, the lower was the wear. With increased volume of reinforcement the wear mechanism of composites changed from the adhesive to the fatigue/delaminating one. The wear of the cast-iron counter sample was several times higher than that for P/M composites. Considering the life of the piston-piston ring couple, the piston composite with 10 vol% Al₂O₃ appears to be the best. The rate of clearance development for this couple is twice as low as that for the conventional piston alloys.     

Dry sliding wear behaviour at ambient and elevated temperatures of plasma transferred arc deposited aluminium composite coatings

Abstract

Plasma transferred arc (PTA) surfacing is a surface engineering process in which a coating is deposited on the substrate by the injection of metal powders and/or ceramic particles into the weld pool created by the formation of a plasma plume. The present work involved the tribological evaluation of metal matrix composite (MMC) coatings deposited onto an aluminium alloy using the PTA technique. Coatings were fabricated by the deposition of an Al–Ni powder containing either Al₂O₃ or SiC particles. Dry sliding wear behaviour of the coatings was evaluated at ambient and elevated temperatures. Under sliding conditions of low applied stress and ambient temperature, reinforcement properties such as interfacial structure and fracture toughness have a significant influence on wear resistance. The SiC particles, which exhibit high interfacial bonding and toughness, support the matrix by acting as load bearing elements, thereby delaying the transition in wear mechanism as applied stress increases. As applied stresses exceed the fracture strength of the SiC and Al₂O₃ particles, these particles suffer fragmentation and/or debonding and no longer support the matrix. At higher stresses and elevated temperature, matrix properties such as flow stress and the tribolayer formation play more important roles in determining wear resistance.     

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.     

Synergistic effects of TiC and graphene on the microstructure and tribological properties of Al2024 matrix composites

Al matrix composites have attracted significant attention of researchers in recent years due to their lightweight, excellent mechanical and tribological properties. In this study, an Al2024 matrix hybrid composite (AMHC) reinforced with both TiC nanoparticles and graphene nanoplatelets (GNPs) was produced via a route of powder metallurgy. And its microstructure, microhardness and tribological properties are compared with those of unreinforced Al2024 alloy matrix and Al2024 matrix composites reinforced with either only TiC or GNPs. It was found that the distribution of Al₂Cu, TiC nanoparticles and GNPs in the matrix and the wear resistance are significantly improved when introducing both TiC nanoparticles and the GNPs. The wear mechanisms change from the adhesion-dominant wear for Al2024 and the other singly reinforced composites into abrasive-dominant wear for the hybrid composite. The significantly improved wear resistance of the AMHC is attributed to the synergistic effects of reinforcing and self-lubricating of the TiC and GNPs.     

Si、Ti、Mo添加剂对自蔓延防护涂层性能的影响

为了提升自蔓延涂层的各项性能,拓宽自蔓延涂层的应用领域,本文实验制备了两种自蔓延防护涂层,即Al和Fe₂O₃的自蔓延铝热涂层和含有Si、Ti、Mo添加剂的低温自蔓延铝热涂层,借助X射线衍射、扫描电子显微镜等技术对不同成分涂层的组织形貌和物相组成进行了对比分析。利用显微硬度计、万能实验机、多功能摩擦磨损试验机研究了两种涂层的力学性能和摩擦性能。研究表明,添加剂使得涂层的孔隙率降低了66.7%,结合强度提高32.3%,常温下显微硬度提高17.6%,断裂韧性提高了28%,耐磨性能提高约25%。两种涂层均呈现出以Al₂O₃相为主的陶瓷层、金属过渡层与基体的3层结构,Si、Ti、Mo添加剂使得涂层中出现了SiC、TiC、MoSi₂等硬质相,且反应更为充分,结合强度、硬度、断裂韧性、摩擦性能均得到提升。     

Superior high-temperature resistance of aluminium nitride particle-reinforced aluminium compared to silicon carbide or alumina particle-reinforced aluminium

Aluminium-matrix composites containing AlN, SiC or Al₂O₃ particles were fabricated by vacuum infiltration of liquid aluminium into a porous particulate preform under an argon pressure of up to 41 MPa. Al/AlN had similar tensile strengths and higher ductility compared to Al/SiC of similar reinforcement volume fractions at room temperature, but exhibited higher tensile strength arid higher ductility at 300–400 °C and at room temperature after heating at 600 °C for 10–20 days. The ductility of Al/AIN increased with increasing temperature from 22–400 °C, while that of Al/SiC did not change with temperature. At 400 °C, Al/AlN exhibited mainly ductile fracture, whereas Al/SiC exhibited brittle fracture due to particle decohesion. Moreover, Al/AlN exhibited greater resistance to compressive deformation at 525 °C than Al/SiC. The superior high-temperature resistance of Al/AlN is attributed to the lack of a reaction between aluminium and AlN, in contrast to the reaction between aluminium and SiC in Al/SiC. By using Al-20Si-5Mg rather than aluminium as the matrix, the reaction between aluminium and SiC was arrested, resulting in no change in the tensile properties after heating at 500 °C for 20 days. However, the use of Al-20Si-5Mg instead of aluminium as the matrix caused the strength and ductility to decrease by 30% and 70%, respectively, due to the brittleness of Al-20Si-5Mg. Therefore, the use of AIN instead of SiC as the reinforcement is a better way to avoid the filler-matrix reaction. Al/Al₂O₃ had lower room-temperature tensile strength and ductility compared to both Al/AlN and Al/SiC of similar reinforcement volume fractions, both before and after heating at 600 °C for 10–20 days. Al/Al₂O₃ exhibited brittle fracture even at room temperature, due to incomplete infiltration resulting from Al₂O₃ particle clustering.     

Microstructure and mechanical properties of TiCAl2O3 coatings

The microstructure, phase distribution and hardness of TiCAl₂O₃ two-phase coatings prepared by high rate physical vapor deposition have been studied as functions of deposition temperature and feed composition. Structural analysis using X-ray diffraction shows that the coatings consist of α-Al₂O₃ and TiC (cubic) phases. Transmission and scanning electron microscopy have been used to study the distribution of the two phases in the coatings. The growth morphology is fine grained at low temperatures and becomes a dense columnar type at high temperatures of deposition. The microhardness shows a corresponding increase with deposition temperature. Details of the relationship between the microstructure, composition and hardness of the coatings are reported.     

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.     

Investigation on in situ Al0.5FeSi0.5/Al composites prepared by transient liquid phase sintering

In situ Al_0.5FeSi_0.5/Al composites were prepared by transient liquid-phase sintering. The hardness and wear resistance of the composites were investigated with an XHV-1000 microhardness tester and an M-2000 wear tester. Results show that with increased sintering temperature and holding time, the in situ needle-like reinforcement is transformed into short, bar-like, massive particles. At a sintering temperature of 510 °C and holding time of 4 h, the reinforcement consists of short, bar-like Al_0.5FeSi_0.5; moreover, the hardness of the in situ Al_0.5FeSi_0.5/Al composites peaks to a value eight times that of pure aluminum and 2.5 times that of Al–Si alloy. Accordingly, the wear resistance of the composites is the highest, i.e., 6.6 that of pure Al and 4.5 times that of Al–Si alloy.     

A study of the tool life of TiC and TiC plus Al2O3 chemical vapour deposited tungsten carbide tools

Tool life characteristics were investigated for tungsten carbide cutting tools coated with TiC and with TiC plus Al₂O₃. A low carbon steel workpiece was turned on a lathe at a feed rate of 0.206 to 0.410 mm rev^–1 and a depth of cut of 0.1 to 0.5 mm for cutting velocities between 100 and 250 m min^–1. Data were analysed using both Taylor's tool life equation and Wu's tool life method. Results were similar for both methods but Wu's method seemed to give more consistent results. Compared to an uncoated tungsten carbide tool, the tool life of both the coated tools were from 5 to 7 times longer and the improvement was greater at higher cutting speeds. The TiC plus Al₂O₃ coated tool was slightly superior to the TiC coated tool. The wear mechanism and a possible explanation of increased tool life for the coated tools are discussed.     

Effect of C/Ti ratio on the laser ignited self-propagating high-temperature synthesis reaction of Al-Ti-C system for fabricating TiC/Al composites

TiC/Al composite was successfully synthesized utilizing laser ignited self-propagating high-temperature synthesis (SHS) of Al-C-Ti system with the different C/Ti molar ratio. When the molar ratio of C to Ti is below 1:1 in the starting materials, in addition to fine TiC particulates, a large amount of Al₃Ti phase was found in the composites; however, when the molar ratio of C to Ti is 1:1 in the starting materials, the Al₃Ti phase was almost completely eliminated and the distribution of TiC particulates generally appeared to be more homogeneous throughout the products synthesized.     

Wear behavior of TiB<Subscript>2</Subscript> inoculated 20Cr–3Mo–4C high chromium white cast irons

FeTi, B₂O₃, Al, and FeW particulates, approximately 40–60 μm in size, were mixed in stoichiometric ratio and sintered at 1,200 °C. The sintered particulates were added as 5 wt% to molten high chromium white cast iron over 50 C-deg above the melting temperature, and stirred at 1,000 rpm. The samples were investigated in three groups: (1) high Cr white cast iron inoculated by the particulates sintered from Al–FeTi–B₂O₃ particulates; (2) high Cr white cast iron inoculated by the sintered particulates derived from Al–FeTi, B₂O₃, and FeW particulates; and (3) specimens of the second group that were subsequently homogenized. The microhardness of ceramic particulates was measured as 2,800–3,400 HV₁₀. The effect of sintered particulate volume fraction on the abrasive wear resistance of the high chromium white cast iron was determined. The wear resistance and hardness of the composites improved significantly as a result of particulate inoculation. The application of the homogenization heat treatment to the inoculated samples produced a microstructure having homogeneously distributed particulates.