【作者】 金志新；

【导师】 王武孝；

【作者基本信息】 西安理工大学 ， 材料科学与工程， 2008， 硕士

【摘要】 本文采用无压浸渗方法制备了Al₂O₃纤维增强AZ91D镁基复合材料。采用金相显微镜、SEM（扫描电镜）、XRD（X射线衍射）和EDS（能谱分析）等检测分析手段,对复合材料的组织、力学性能及摩擦磨损行为进行了研究。经过工艺优化得到的预制体通过扫描电镜观察,发现其内部存在大量的微观孔洞;通过测定预制体的孔隙率,其值可达72%以上;孔隙率随造孔剂碳粉质量分数的增加而增大,当碳粉质量分数小于20wt.%时,随碳粉质量分数的增加,孔隙率变化较明显。碳粉质量分数大于20wt.%时,孔隙率变化幅度趋于平缓。通过不同工艺条件下的浸渗成形实验发现,在保温温度高于635℃、保温时间大于40min时浸渗成形均可完成。复合材料的组织中除了存在长条状与点状的Al₂O₃纤维及镁基体外,还可以发现少量的微观孔洞和生成的Mg₂Si相;随着保温温度的升高或保温时间的延长,微观孔洞的数量有所减少,同时,Mg₂Si相的数量也有所增多、尺寸略有变大,并对复合材料的硬度有较明显的影响。Al₂O₃纤维与Mg基体界面处结合良好,界面附近存在Mg₂Si:Al₂O₃纤维表层附着有一层颜色较深的膜,经能谱分析判断其为MgO。增大Al₂O₃纤维的加入量,复合材料硬度呈现上升趋势,且复合材料的硬度都高于AZ91D镁合金的。硬度随保温时间变化趋势是平缓上升的,随着保温温度变化趋势是先升高后平缓降低。复合材料的摩擦磨损实验中发现存在一个由轻微磨损向急剧磨损转化的临界载荷,随着Al₂O₃纤维体积分数的增加,该临界转变载荷逐渐升高。Al₂O₃纤维含量对复合材料的磨损率的影响存在临界值,临界点就在Al₂O₃纤维18 vol.%时出现。随着载荷的增加,磨损机制从低应力磨料磨损和轻微粘着磨损向严重的高温粘着磨损转变。随纤维体积分数的增加,复合材料的磨损机制由粘着磨损向低应力磨料磨损和轻微粘着磨损转变。纤维18vol.%复合材料从轻微磨损到急剧磨损的临界转变温度为250℃,在低温时磨损机制为以磨料磨损为主,轻微粘着磨损为辅;随着温度的升高,粘着磨损加剧,并最终发展为严重的高温粘着磨损。更多还原

【Abstract】 In the paper,Al₂O_3f/AZ91D composite was prepared by using the method of Pressureless Infiltration process,Its microstructure,mechanical properties,friction and wear behaviour were studied by Optical microscope,SEM,XRD and EDS.Large numbers of micro-porosities in the preform made after optimizing the process could be seen in the SEM picture.Porosity of the preform was more than 72%,and it increased with increasing mass fraction of carbon powder.When mass fraction of carbon powder was less than 20wt.%,Porosity changed evidently with increasing in the mass fraction.In contrast,when mass fraction of carbon powder was more than 20wt.%,the change extent of Porosity became flat.It was discovered that infiltration and forming in the experiment could be accomplished as holding temperature higher than 635℃and holding time longer than 40min.Besides Al₂O₃ fiber with long-rod and spotty shape and Mg matrix,a small quantity of micro porosity and Mg₂Si phase could be seen in microstructure of the composite also.With increasing in holding temperature or holding time,the amount of micro porosity decreased while the amount and dimension of Mg₂Si phase increased which impact hardness of the composite evidently.Al₂O₃ fiber and Mg matrix combined well at the interface where Mg₂Si exist nearby.A layer film with deeper color on the surface of Ao₂O₃ fiber was judged for MgO by EDS analysis.With increasing of Al₂O₃ fiber content,hardness of composite present a up-trend and was greater than AZ91D magnesium alloy.Change trend of the hardness rose gently with increasing of holding time,while it declined gently after increased with increasing of holding temperature.Critical load from slight wear to severe wear was found in friction and wear experiment. With increasing of Al₂O₃ fiber volume fraction,the critical transformation load increased.A critical value about the wear rate of composite which was affected by Al₂O₃ fiber content existed,it appeared when the volume fraction of Al₂O₃ fiber was 18 vol.%.With applied loads increasing,the wear mechanism changed from low stress abrasion and slight adhesive wear to severe high temperature adhesive wear.With fiber volume fraction increasing,the wear mechanism of composite changed from adhesive wear to low stress abrasion and slight adhesive wear.When fiber volume fraction was 18vol.%,the critical transform temperature from slight wear to severe wear of composite was 250℃.During low temperature period,the abrasion wear took as the dominant and the slight adhesive wear as the subsidiary.With increasing the temperature adhesive wear became severe and finally turned to high temperature severe adhesive wear.更多还原