无压烧结Ca_3(PO_4)_2/Si_3N_4复合陶瓷的组织结构与性能

以Ca_3(PO_4)_2和Si_3N_4为原料,采用无压烧结的方法制备Ca_3(PO_4)_2/Si_3N_4系列复合陶瓷.复合材料中Ca_3(PO_4)_2能与Si_3N_4稳定共存,烧结后未发现有新相生成.随着烧结温度的提高,复合材料的致密度和β-Si_3N_4的相对含量也随之升高,柱状β-Si_3N_4晶粒的生长更加充分,晶粒相互搭接、交织.复合陶瓷的力学性能随着烧结温度的提高而升高,1700 ℃无压烧结复合材料的抗弯强度达到547 MPa,断裂韧性达到7.3 MPa·m~(1/2),从断口照片中可以观察到β-Si_3N_4晶粒的拔出和桥联作用.通过加热试样并在水中骤冷后测弯曲强度的方法,表明Ca_3(PO_4)_2/Si_3N_4复合材料具有良好的抗热震性能.     

比表面积对β-Si_3N_4与SiO_2反应生成Si_2N_2O的影响

以铁合金行业的副产物-硅微粉(SiO_2≥90%,质量分数)和闪速燃烧合成的β-Si_3N_4(β-Si_3N_4≥95%,质量分数)为原料,按质量分数β-Si_3N_4:SiO_2=2:1的比例,分别将比表面积为1.19, 1.67, 2.48 m~2/g的β-Si_3N_4与SiO_2均匀混合、成型,分别经1300、1400、1500、1600 ℃,3 h埋碳(不接触碳)热处理,并对自然冷却后试样进行XRD、SEM分析.结果表明,β-Si_3N_4与SiO_2从1300 ℃开始缓慢反应生成Si_2N_2O,随温度升高到1500 ℃以上时Si_2N_2O反应速度明显加快;在1300、1400 ℃,反应以固-固反应为主,β-Si_3N_4的比表面积对Si_2N_2O生成量的影响越大,比表面积大则Si_2N_2O生成量较高;在1500 ℃以上时,随着硅微粉收缩、液化,将β-Si_3N_4包裹、胶结到一起,反应方式以固-液反应为主,反应速度明显加快,加速了Si_2N_2O的形成,β-Si_3N_4的比表面积对Si_2N_2O生成量的影响不明显.     

晶相组成对Si_3N_4陶瓷介电性能的影响

以MgO-Al_2O_3-SiO_2(MAS)体系作为烧结助剂,采用无压烧结,通过控制烧结工艺,制备出具有不同晶相组成的Si_3N_4陶瓷.研究了晶相组成对氮化硅陶瓷微波介电性能的影响.借助XRD、SEM对Si_3N_4陶瓷微观组织进行了研究.结果表明:在烧结过程中,有中间相Si_2N_2O产生;经1850 ℃、0.5 h烧结,β-Si_3N_4全部转变为具有较大长径比,显微结构均匀的长柱状β-Si_3N_4晶粒;Al~(3+)和O~(2-)能够进入β-Si_3N_4晶体内形成β-Si_(6-x)Al_xO_xN_(8-x)固溶体,使晶体内部产生较大的空隙或晶格畸变,在外电场作用下,易于产生离子位移极化,导致介电常数升高;同时,随着烧结温度的提高,存在于晶界的玻璃相含量增加,试样的介电常数随之升高.     

MECHANICAL PROPERTIES AND INTERFACIAL STRUCTURES OF ALUMINIUM BORATE WHISKER REINFORCED ALUMINIUM COMPOSITES

Quality 9Al_2O_3-2B_2O_3 whisker reinforced 6061Al or Al composites have beenprepared by technique of squeeze casting.The mechanical properties of the9Al_2O_3·2B_2O_3(w)/6061Al composites could be hardly improved by T6 treatment,owingto cause the remarkable interracial reaction.An observation under high resolution trans-mission electron microscope on interfaces shows that the serious chemical reaction occursand the product is Al_2MgO_4.But no such reaction is found at the interfaces of 9Al_2O_3.2B_2O_3(w)/Al composite.EDS analysis on the interfaces shows that above mentionedinterracial reaction may be resulted from the interracial segregation of Mg atoms in6061Al matrix during sequeeze casting.     

Effects of silicon,magnesium and strontium content on the qualities of Al-Si-Mg alloys

According to the specification of AA standard, the magnesium content of 356.1 alloy ranges from 0.25 to 0.45%. In producing Al-Si-Mg alloy the strontium content for the modified 356 (Al-7%Mg) alloy might range from 0.005 to 0.02%. Therefore, 356 alloys might be produced with different percentages of Mg and/or Sr. The effects of changes in Si content (from 6.6% to 10.8% in gravity casting and 6.5% to 10.3% in squeeze casting), Mg content (from 0.36% to 0.48% in gravity casting and 0.3% to 0.44% in squeeze casting), and Sr content (from 0.0007% to 0.0158% in gravity casting and 0.0015% to 0.04% in squeeze casting) on the microstructures, density, mechanical properties and strength of different Al-Si-Mg alloys were fully investigated and discussed. Different melts were poured in the ASTM B108 permanent mould and dies in a vertical squeeze machine to produce bar castings. These bar castings were then machined and the mechanical properties tested. Experimental results showed that if a high strength and a high elongation were desired in a squeeze casting after T6 treatment, an increase in Si and Sr content to 9.9% and 0.019% (Mg at 0.3%) would lead to 280 MPa strength, 12% elongation and Weibull modulus of 34 in reliability of strength. If both strength and reliability were desired in a squeeze casting after T6 treatment, an increase in Si content to 10.3% (Sr at 0.0015% and Mg at 0.3%) would result in 294 MPa strength, 8.7% elongation and a great Weibull modulus of 67. In gravity casting, after T6 treatment, increasing Si content to 10.4–10.55% and Sr content in the range of 0.0007–0.0208% and 0.35% Mg could develop 282–284 MPa strength at about 6.6% elongation with Weibull modulus of around 31. In Al-7Si-Mg alloy, increasing Mg content from 0.26% to 0.48% decreased the tested elongations of both as-cast and heat treated squeeze castings and gravity castings.     

PREPARATION,PROPERTIES AND INTERFACE STRUCTURES OF Si_3N_(4w)/6061Al COMPOSITE

The Si_3N_4 whisker reinforced 6061Al composite with bending strength of 790 MPa wasprepared by squeeze casting process.After heat-treatment under T6 regime i.e.530℃,1 h solutioning and 160℃,24 h aging,an increment in strength and microhardnessmay be over 20% and 28% respectively,The microstructures of Si_3N_4 whisker andSi_3N_4/Al interface were observed by meas of HRTEM.The relation between interracialstructure and composite properties was discussed.     

稀土Lu_2O_3增强氮化硅陶瓷的结构与性能

以稀土氧化物Lu_2O_3作为单一添加剂,研究在热处理过程中,稀土氧化物对氮化硅在粉体状态下相变的影响.指出氮化硅粉体的α→β相变率与稀土氧化物的添加量、粉体的热处理温度之间的关系.发现热处理温度在1650 ℃以下时,氮化硅粉体的相变率随着添加剂含量的异常变化.以上述制备的β-氮化硅晶种,在不进行化学处理的情况下直接用于氮化硅陶瓷的增韧,使得所制备的氮化硅陶瓷在保持原有的室温强度基本不变的情况下,断裂韧性得到大幅度提高.在此体系中研究了β-氮化硅晶种的增韧效果及机制.分析了晶粒尺寸及其分布与氮化硅陶瓷性能及显微结构之间的关系.研究表明:以Lu_2O_3为单一添加剂的自增韧氮化硅陶瓷,晶种的加入使材料在保持强度的同时,断裂韧性提高了10%～20%.     

HIGH STRAIN RATE SUPERPLASTICITY IN A SiC_w/2024Al COMPOSITE MADE BY SQUEEZE CASTING

1.IntroductionHighStrainratesuperplasticity(HSRS)infineceramicwhiskerorparticulatereinforcedaluIninUIncompositesisveryattractipeforcommercialaPplicationsbecausetheHSRScompositesusuallyeallibitatotalelongation0f25M00%atahighstrainrate0f>10-2s-1Il-7]andoneofcurrentdrawbacksinsuperPlasticformingteclm0logyisaslowf0rIIilngratewhichistypically10-5-10-3s-1.Forindustrialfabricati0nofceramicwhiskerreinforcedaJumintuncomposites,squeezec88tingprocedureismorecost-ethetivethanpowdermetallurgy(P/M)m…     

发泡法燃烧合成β-氮化硅粉体及其形貌

机械活化后的Si粉加入发泡剂溶液,搅拌、烘干后得到多孔预制坯体.将坯体在流动氮气氛中引发燃烧合成反应.通过调整原料粉体机械活化时间及预制坯体中稀释剂的含量,制得了不同粒径和长径比的氮化硅粉体.利用XRD和SEM对产物的主要成分和形貌进行了表征.实验结果表明,通过发泡法燃烧合成可制备长径比可控、晶粒发育完全的氮化硅粉体.与传统燃烧合成制备的氮化硅粉体相比,发泡法制备的氮化硅粉体结晶度高,形貌均一性好.     

挤压铸造铝基复合材料的高应变速率超塑性

用挤压铸造、挤压比仅为１０∶１的挤压以及进一步的轧制成功地制备了具有高应变速率超塑性行为的βＳｉＣ晶须增强ＬＹ１２复合材料。该复合材料晶粒细小,约为２μｍ;在温度为８０３Ｋ和初始应变速率为１．１×１０－１ｓ－１时,延伸率达３５０％,应变速率敏感系数ｍ值约为０．３５;超塑性变形的主要机制是细小晶粒的晶界滑动,适当的微量液相有利于该复合材料的高应变速率超塑性。     

细晶1420铝锂合金超塑性能试验研究

文章以采用双级时效制度和转向轧制工艺制备的细晶1420铝锂合金为研究对象,通过恒应变速率超塑拉伸试验,研究了合金的单轴超塑拉伸性能。结果表明,在460℃~520℃温度条件下和1×10-4s-1~5×10-3s-1应变速率范围内,细晶1420铝锂合金表现出良好的超塑性,在温度460℃、应变速率1×10-4s-1条件下,延伸率达到650%。利用光学显微镜和透射电镜等检测手段,对超塑变形后材料的组织进行了观察和分析。     

Mg-7.0Al-0.2Zn合金的超塑性及其变形机制

研究不具有典型细晶组织的挤压态Mg-7.0Al-0.2Zn(AZ70)合金的超塑性及其变形机制。结果表明:AZ70镁合金具有良好的超塑性变形行为。在380℃及1×10-3s-1的最佳变形条件下,最大伸长率为191.5%。380℃时具有良好的高应变速率(1×10-2s-1)超塑性变形能力,伸长率为161.5%。晶粒尺寸随温度的升高与应变速率的降低而增大。超塑性变形是以晶界滑移为主,表现为变形过程中晶粒组织基本保持等轴,且孔洞沿晶界形成并长大。同时孔洞的长大及连接导致最终断裂,断口形貌显示为典型的韧窝断裂特征。     

Effect of fabrication method on the aging behavior of 6061 Al matrix composites reinforced with SiC whiskers

Age hardening behaviors of SiC whisker reinforced composites with 6061 Al matrix fabricated by P.M. (powder metallurgy) and squeeze casting were investigated to examine the effect of the fabrication method on the aging kinetics. In the squeeze cast composite, numorous triangular particles which is believed to be MgAlp₂O₄ were observed at Al/SiC interfaces whereas no visible interface particles were observed in the P. M. composite. P.M. composite showed faster age hardening and reached the maximum hardness earler than the squeeze cast composites. The decrease of the aging kinetics in squeeze cast 6061 Al matrix composites compared to that in P.M. composites is thought to result from more severe depletion of Mg atoms due to interfacial reactions in squeeze cast composites. The uniformity of whisker distribution is suggested to influence the general aging behavior through its effect on the local dislocation density. Data on the aging kinetics and the interfacial reactions in other Al alloys were also examined to study various factors which can influence the aging kinetics.     

钛合金激光焊缝的超塑性变形行为及显微组织

通过高温拉伸试验研究Ti-6Al-4V(TC4)合金激光焊缝的纵向超塑性变形行为,采用扫描电镜观察超塑性变形前后焊缝的显微组织.结果表明:TC4钛合金激光焊缝具有良好的超塑性变形能力,在900 ℃、10~(-3) s~(-1)工艺条件下伸长率达到最大值397%;在超塑性变形过程中,原始焊缝的针状马氏体首先转变为片层状的α+β组织,而后片层组织发生再结晶等轴化;随着变形温度升高或应变速率降低,等轴化程度增大.     

预制块制备对挤压铸造SiCW／ZM5复合材料性能的影响

制备了含不同粘结剂的ＳｉＣ晶须预制块,并采用挤压铸造法制备出含不同粘结剂的ＳｉＣｗ／ＺＭ５镁基复合材料,对其组织结构和力学性能进行了研究。结果表明,采用含酸性磷酸铝粘结剂制备的ＳｉＣｗ／ＺＭ５镁基复合材料的性能最佳,这可能和粘结剂与晶须以及基体合金的界面反应有关     

浇注温度对连续碳纤维增强Al-10Mg基复合材料组织和力学性能的影响

通过双辊铸轧工艺制备了连续碳纤维增强的铝镁（10% Mg,质量分数）基复合材料,其中碳纤维的体积分数是6.8%。对不同浇注温度（943、963、983和1003 K）下获得的复合材料的组织和力学性能进行了研究。通过在碳纤维表面上电镀镍涂层以抑制脆性相Al₄C₃的形成。结果表明：碳纤维与铝镁基体具有相对较好的浸润性,并且没有形成Al₄C₃脆性相。随着浇注温度的升高,复合材料的抗拉伸强度（UTS）先升高后降低。当浇注温度为963 K时,复合材料的抗拉伸强度达到了185 MPa,比基体材料（131 MPa）提高了41.2%。此外,对复合材料的拉伸断面进行研究,进一步证实了碳纤维与铝镁基体之间良好的界面结合。双辊铸造法是制备碳纤维增强铝镁基复合材料的有效方法,且具有良好的研究前景。     

不同压力对挤压铸造Al-Cu-Mg合金性能的影响

使用挤压铸造工艺制备了高强、高韧Al-4.5Cu-1Mg合金。在挤压力为70MPa下成型后,合金的最大抗拉强度达到288.8MPa、伸长率达到12.8%、HRB硬度达到48.3。通过对该合金力学性能及其显微组织的研究表明,合金的抗拉强度、伸长率以及硬度随着压力的增加而增大,并且在70MPa时达到最大值,70MPa之后继续增加压力,对材料性能影响不大。研究了挤压力对合金的密度和导电性的影响。试验结果表明,合金的密度随着压力的增加而快速增大,在挤压压力为70MPa时达到最大值,然后变化不大。     

Ti-15-3在β相区的两段超塑性行为研究

研究了应变速率变化时粗晶Ti-15-3板材在β相区的超塑性。第一段的应变速率分别为1×10-1和1×10-2 s-1,应变量为0.2～0.6。在第二段的应变速率为3×10-4 s-1时,获得345%最大伸长率,比在恒应变速率下的伸长率大93%。而两段应变速率下,应变速率敏感系数m值无太大变化。研究了第一段变形结束时动态再结晶晶粒大小和后续超塑性的关系。     

原位生成Al2O3增强Al-4Mg基复合材料中的Al2O3/Al位向关系

综合搅拌铸造法和原位反应制备了Al2O3颗粒增强Al-4Mg基复合材料，并对制备的Al-4Mg基复合材料进行了透射电镜(TEM)观察分析，发现Al2O3／Al之间不存在固定的位向关系，但存在如下优先的位向关系：(1210)Al2O3∥(111)Al，[1012]Al2O3∥[112]Al，[2021]Al2O3∥[101]Al．     

STUDY OF K_(2)O·6TiO_(2) WHISKER REINFORCED AI COMPOSITES FOR THEIR MECHANICAL PROPERTIES AND INTERFACIAL STRUCTURES

A newly developed whisker K_2O 6TiO_2 reinforeed 6061Al composite was prepared bysqueeze casting process.The flexural strength of the composite is 518MPa,and deereasesto 490MPa after T6 treatment.The hardness of the composite also shows the similarchange while T6 treating.The results of HRTEMobservation may explaine this property.change.It was considered that there is a continuous TiO layer at the whisker-matrix inter-face,which is easily to react with the segregated Mg and to form MgTi_2O_4,MgAl_2O_4.Thethickening of TiO layer after T6 treatment is the main reason resulting is strength degra-dation of composite.