The Wear Behavior Of The Nano-sized Tic_p/Al-Cu Composites

Aluminum matrix composites are promising materials for potential applications in many industrial fields, such as electronics, automotive, aerospace, and defense, due to their low weight, high specific strength, high specific stiffness and high wear resistance. Friction wear property is the important factor which influences the performance and service life of aluminum matrix composites. Especially the dry friction wear in high-speed and high-load working conditions, and high-temperature hostile environments requires a high friction wear resistance. Because of the high hardness and high wear resistance of ceramic particles, the wear resistance of ceramic particles reinforced aluminum matrix composites is expected to be improved. It has been reported that micron-sized ceramic particles reinforced aluminum matrix composites show higher tensile strength but lower ductility, and the improvement in high temperature performance is not obvious. On the other hand, the addition of nano-sized ceramic particles could improve the strength and ductility simultaneously, and the improvement in high-temperature tensile strength is obvious. Nevertheless, studies on the dry friction wear performance, especially at high-temperature, of nano-sized particle and bimodal size particle reinforced aluminum matrix composites are few. Thus, the the factors which influence the dry friction wear performance of nano-sized particle and bimodal size particle reinforced aluminum matrix composites need more study.In this thesis, the Al-Cu alloy was selected as matrix alloy, and TiC particle was used as reinforcement, combining the advantage of stirring casting and SHS, in situ TiC_p/Al-Cu composites were fabricated by stirring casting method using master alloy. The influence of nano-sized TiC_p on the room-temperature and high-temperature friction wear performance was studied, as well as the mechanism. The high-temperature friction wear performance of in-situ micron-sized and bimodal size TiC_p/Al-Cu composites was also investigated.The main results are as follows:(1) Nano-sized/micron-sized/nano-micron bimodal sized TiC_p/Al-Cu composites were fabricated by stirring casting +nano-sized /micron-sized TiC_p-Al master alloy method. the addition of TiC_p could refine α-Al grains significantly. The average grain diameter of the matrix alloy was 160μm, while the average grain diameter of the nano-sized TiC_p/Al-Cu composites was 40-50μm.(2) It is revealed that the addition of nano-sized Ti C particles could improve the strength and ductility of the composites simultaneously. The improvement in high temperature tensile property was obvious. At room temperature, the tensile strength and elongation after fracture of 0.7wt.% TiC_p/Al-Cu composites reached 573 MPa and 14%, respectively, increased by 18.1% and 112.1%, compared with the Al-Cu matrix alloy. At higher temperatures, the improvement of tensile strength was more obvious. At 180℃, 200℃ and 220℃, the tensile strength and elongation after fracture of 0.7wt.% TiC_p/Al-Cu composites reached 407 MPa and 18.1%, 399 MPa and 19.6%, 338 MPa and 18.7%, increased by 32.6% and 229.1%, 53.4% and 216.1%, 36.3% and 101.1% compared with the matrix alloy, respectively.(3) It is revealed that the addition of 0.1wt.%-2.0wt.% nano-sized TiC particles could enhance the wear resistance of composites significantly. At room temperature, the wear resistance of 0.5wt.% TiC_p/Al-Cu composite was 58% higher than the matrix alloy. At 180℃-220℃, the wear resistance of 2.0wt.% TiC_p/Al-Cu composite was increased by more than 180% compared with the matrix alloys.(4) It is revealed that at room temperature, the wear resistance of 0.5wt.% nano-sized TiC_p/Al-Cu composite was 40% higher than the matrix alloy under the condition:20N load, 10 min wear time,100-400r/min rotation speed.and, the wear resistance of 0.5wt.% nano-sized TiC_p/Al-Cu composite was increased by more than 50%(at room temperature) and 60%(at 180℃) compared with the matrix alloyunder the condition:200r/min rotate speed, 10 min wear time, 10-40 N load.(5) It is revealed that the friction wear resistance of the materials tested at 180℃,ranked in descending order are as follows:1.0wt.% micron+0.5wt.% nano bimodal sized TiC_p reinforced compositesâ†'0.5wt.% nano-sized TiC_p reinforced compositesâ†'1.0wt.%-5.0wt.% micron sized TiC_p reinforced compositesâ†'Al-Cu matrix alloy.(6) The dry sliding wear behavior of the matrix alloy and composites at room temperature and high temperatures is investigated. The wear modes at room temperature are mainly as follows: adhesive wear, abrasive particles wear and mild oxidation wear. At elevated temperatures, when the wear temperature is lower than 140℃, the wear modes are mainly adhesive wear, abrasive particles wear and mild oxidation wear. When the wear temperature is higher than 140℃, the wear modes are oxidation wear, fatigue wear and abrasive particles wear. The improvement in the wear resistance of materials by nano-sized TiC_p is attributed to the refined grain structure and Orowan strengthening, which improve the strength, ductility and hardness.