Study On Preparation And Properties Of Cu Matrix Composites Reinforced With Alumina Whisker

With high elastic modulus,chemical and thermal stability,alumina whisker is a kind of artificially controlled synthetic material.It is an excellent reinforcement and expected to improve the performance of composite.According to the relevant literatures,the research on alumina whiskers is still in the preparation stage,there are not many reports on composite materials.In this paper,the content of alumina whisker is taken as the research variable,copper matrix composites reinforced with different content of alumina whisker were prepared by mechanical alloying and powder metallurgy,micro-structure,mechanical and tribological properties were systemly investigated.Based on these studies,strengthening and fracture mechanisms by multiple reinforcements were analyzed to provide some valuable references and significant theories to design and prepare new Cu-matrix composite materials.Firstly,sodium lauryl sulfate aqueous solution?2.0g/L?was used to ultrasonically treat the alumina whiskers,then alumina whiskers were mixed with copper powders,alloy powders and so on,composite powders were ball-milled,followed by freeze-drying,and the first batch of the obtained composite powder is subjected to cold press forming,followed by hot isostatic pressing.The second batch of composite powder is subjected to hot press sintering and hot isostatic pressing.After sintering,Optical microscopy?OM?,scanning electron microscopy?SEM?and transmission electron microscopy?TEM?were used to observe the microstructure and structure of the composites,and the mechanical properties and friction and wear properties of the composites were tested.The experimental results show that with the increase of Al₂O₃ whiskers,the hardness of the composite material decreases slowly at first and then decreases sharply after the molding and hot isostatic pressing sintering.When the content of Al₂O₃ whiskers is 1.0 wt.%and 1.5 wt.%,the hardness sharply decreased from 107.3 HV to 47.2 HV and 56.5 HV,and the compressive strength also showed a similar trend.The main reason of there phenomena was the aggregations of graphite and Al₂O₃ whiskers.In order to improve the performance of composites,the experimental formula and preparation process were changed.The Al₂O₃whisker and particle co-reinforced copper matrix composites were prepared by hot pressing and hot isostatic pressing.The results show that the density and hardness of the composites decrease slightly with the increase of Al₂O₃ whisker content.The strength of the composite increases with the increase of Al₂O₃ whisker content.When the Al₂O₃ whisker content is1.5wt.%,the compressive strength of the composite reaches a maximum value of288.26MPa.The friction and wear tests were carried out on the samples after hot pressing and hot isostatic pressing.The results of the orthogonal experiments show that with the increase of the content of Al₂O₃ whisker,the friction coefficient of the composite material first decreases and then increases,which is lower than the initial friction coefficient.The wear amount of the composite material decreases continuously and then tends to be stable,indicating that Al₂O₃ whisker can reduce the friction coefficient of the composite materials.The results of variance analysis show that the Al₂O₃ whisker content and the rotational speed have no significant effect on the friction coefficient and wear,and the load has a significant effect.The composite materials prepared by two different methods have the same strengthening mechanism,which is mainly composed of fine-grain strengthening and solid solution strengthening,and there are also Eurorovin strengthening and dislocation strengthening.The fracture modes are also the same brittle fractures.The weak interface between the reinforcement and the matrix leads to the stress concentration.When subjected to the external load,these locations will induce the initiation of microcracks.At the same time,the microcracks continue to expand under the external force and eventually lead to brittle fracture of the composite material.