电弧熔炼Ti6Al4V/B4C复合材料微观组织与力学性能

采用真空电弧熔炼技术制备了不同含量B₄C的Ti6Al4V/B₄C钛基复合材料,并采用光学显微镜、扫描电子显微镜、显微硬度计、静态压缩及拉伸测试等对其微观组织及力学性能进行了表征分析. 结果表明,电弧熔炼过程B₄C与钛基体原位反应生成TiB,TiC及TiB₂相,TiB呈现一维生长晶须状,TiC呈现颗粒状,在B₄C质量分数为10%时生成块状TiB₂,并可能会形成特殊的中空棱柱状结构Ti(B_xC_y)聚合物. 原位反应生成的TiB₂可显著提高钛基复合材料的显微硬度. 当B₄C质量分数为0.5%时,钛基复合材料原位反应生成的连续网状、均匀分布的TiB和TiC试样具有最优力学性能,试样最大抗压强度值达到1 990 MPa,最大压缩应变为35.5%,压缩性能超过熔炼钛合金,抗拉强度达到1 034 MPa,与熔炼钛合金材料相比提高近24%,但塑性有所降低,并随着B₄C含量增加,抗拉强度逐渐下降,其断裂方式由韧性断裂转变为脆性断裂.     

过渡元素改善B4C/Al材料界面润湿性的机理研究

B₄C/Al复合材料是目前最理想的中子吸收材料,但工业上常用的液态搅拌法制备过程中存在着界面润湿性差的问题。本文结合实验及第一性原理的方法,通过研究Al(111)/AlB₂(0001)和Al(111)/TiB₂(0001)界面的结构来分析工业上添加过渡元素Ti对B₄C/Al界面润湿性的改善机制。通过计算发现,Al(111)/TiB₂(0001)界面相对Al(111)/AlB₂(0001)界面具有更高的粘附功值,说明其界面结合更强。进一步对比Ti掺杂二硼化物和AlB₂的偏态密度结构,发现Ti掺杂体具有较低的反键态,表明Ti-3d和B-2p轨道电子杂化后,在B、Ti原子间形成了较强的化学键,从而促进了Al(111)/TiB₂(0001)界面处的强结合作用,提高了Al(111)/TiB₂(0001)界面粘附功,故而改善了B₄C/Al界面的润湿性。根据同样的理论依据,V掺杂体也具有较低的反键态,V和B之间的强结合效果或许能够改善B₄C/Al界面的润湿性,成为又一理想的溶体改性掺杂元素。     

含微纳B4C/Ti颗粒铜基复合材料的微观组织与力学性能

采用高能球磨(HEBM)和放电等离子烧结(SPS)工艺成功制备出微纳B₄C/Ti颗粒增强铜基复合材料(CTBCs),通过X射线衍射(XRD)、光学显微镜(OM)、扫描电子显微镜(SEM)以及能谱(EDS)等测试手段对其微观组织形貌进行表征。结果表明,(B₄C+Ti)颗粒在基体中均匀分布,增强体与铜基体界面结合良好,且其结合形式为冶金结合和机械结合并存。采用阿基米德排水法测定出烧结态试样的致密度。复合材料的显微硬度、拉伸屈服强度、抗拉强度和延伸率等力学性能相较于纯铜试样得到显著提高,这主要归因于载荷传递、细化晶粒与热错配等强化机制。复合材料的拉伸断口表现出明显的韧性断裂特征。     

SiCw/Al复合材料力学性能分散性

金属基复合材料力学性能分散性影响其性能评价和广泛应用.本文研究了测量方法和组织缺陷对SiCw/Al复合材料力学性能统计分布规律的影响.结果表明,复合材料的弹性模量、强度和延伸率等性能均存在分散性,高性能数据出现频率最高,向低的性能值分散.弹性模量分散性受测量方法影响很大,直线段扩大法可以减小性能分散范围.强度和延伸率性能高的试样中发现夹铝区或未浸渗区等缺陷的概率远低于低性能试样,微观缺陷是造成强度和延伸率向低值方向分散的主要原因.为此减少组织缺陷并合理选择实验方法对复合材料的性能评价和应用是必要的.     

Ti对SiCp/6092铝基复合材料激光焊焊缝组织和性能的影响

采用不同厚度的Ti箔作为填充材料对SiC_p/6092铝基复合材料进行激光焊接,分析不同含量Ti元素对焊缝组织和焊接接头力学性能的影响. 结果表明,Ti箔的加入可以有效改善熔池流动性,从而减少焊缝区的工艺型气孔. 同时,填加Ti箔可以避免激光直接照射在母材上引起的低熔点元素烧损. 在激光的照射下,Ti箔完全熔化并与在热传导作用下部分熔化的母材金属发生冶金反应,Ti元素含量过少时,界面反应得不到有效抑制,焊缝中仍分布有大量的脆性相,Ti元素对焊接接头的力学性能改善不明显;Ti元素含量过多时,Ti元素在熔池中未能扩散开,富余的Ti元素与Al元素反应生成Al₃Ti. 过分长大的Al₃Ti呈片状,将对接头的力学性能不利. 因此,向熔池中加入适量Ti元素有利于改善熔池冶金反应,从而提升接头力学性能,焊接接头的最大抗拉强度可达206 MPa.     

石墨烯/Ti60复合材料组织与力学性能研究

石墨烯与Ti60合金粉末经过球磨混合后,采用放电等离子烧结法(SPS)制备出石墨烯/Ti60复合材料,并在900℃对其进行热轧加工。采用扫描电子显微镜(SEM)、能谱仪(EDS)、金相显微镜和万能试验机对烧结态与轧制态Ti60合金、石墨烯/Ti60复合材料的微观组织和力学性能进行分析。结果表明：添加质量分数为0.1%的石墨烯能够减小复合材料原始β相尺寸,增大α相尺寸。经热轧加工后,石墨烯/Ti60复合材料在室温、600℃和700℃的抗拉强度分别为1353.0、746.6和391.7 MPa,相比Ti60合金分别提高了9.24%、9.46%和2.99%。     

TiC/Ti层状复合材料组织与力学性能研究

为了平衡钛基复合材料（titanium matrix composites, TMCs）的强度和延展性,通过电泳沉积将氧化石墨烯（graphene oxides, GOs）沉积到Ti箔表面,然后进行放电等离子烧结（spark plasma sintering, SPS）制备了具有层状结构的原位TiC/Ti复合材料,并对复合材料进行冷轧和退火处理从而进一步优化复合材料的综合力学性能。结果表明,烧结过程中,Ti箔表面的GOs与Ti基体反应形成了原位TiC,从而形成了TiC/Ti层状复合材料,随着沉积时间的增加,分布在Ti层之间的TiC的含量增加;复合材料经过冷轧和退火后,退火态材料的晶粒为等轴晶,且TiC仍然保持层状分布特征。沉积时间120 s时,烧结态材料的抗拉强度（UTS）为555 MPa,伸长率（δ）为15%;退火态材料的抗拉强度为568 MPa,伸长率为27%,相比于烧结态材料,退火态材料达到了较好的强塑性匹配。此外,基于微观组织及断裂行为的分析对复合材料的强韧化机制进行了讨论。     

挤压铸造Al2O3/Al-4.5Cu复合材料的力学性能研究

研究了挤压铸造短纤维/铝基复合材料中纤维体积分数以及预制件的预热温度对复合材料力学性能的影响。结果表明：纤维加速了复合材料的时效强化过程，随着纤维体积分数的增加，复合材料的硬度、强度、弹性模量增大，而塑性下降；随着预制件预热温度的升高，冷却速度减慢，复合材料的力学性能下降。     

(WC+B4C)p/6063Al复合材料的力学性能研究

以粉末冶金法制备了具有屏蔽效能的铝基复合材料,分别以10∶1、15∶1和25∶1挤压比热挤压,并将挤压后的材料进行固溶强化和时效处理.通过对挤压态和T4态(WC+ B4C)p/6063Al复合材料拉伸性能的比较以及SEM、TEM分析,研究了该复合材料的力学性能.结果表明:以15:1挤压比进行热挤压,在520～530℃下固溶强化和时效处理时,该复合材料的力学性能最佳,抗拉强度大于300MPa且伸长率达10％以上;热处理后基体中Mg2Si析出相尺寸和形貌上的变化以及增强颗粒的弥散强化是该复合材料力学性能提升的原因.     

SPS工艺对GNFs/Al复合材料界面特征及力学性能的影响

利用放电等离子烧结(SPS)技术在不同温度及保温时间条件下制备了石墨烯/铝基复合材料,并对其微观组织及拉伸力学性能进行分析。结果表明,通过改变SPS工艺可调控石墨烯/铝的界面特征,进而影响复合材料的力学性能。500℃烧结时,石墨烯/铝界面反应虽被抑制,但界面结合力较弱,复合材料强度低;烧结温度提高到560℃时,界面结合力明显增强,且通过短时快速烧结可有效控制界面反应的发生,使复合材料力学性能明显提高。此外,石墨烯纳米片还可抑制铝基体晶粒随烧结温度升高而长大。     

Ti6Al4V表面激光熔覆NiCrBSi+B4C涂层的组织结构

选用NiCrBSi及2％民C混粉在Ti6Al4V合金表面进行激光熔覆处理，使基体中的Ti和B4C发生化学反应原位生成TiC、TiB2硬质增强相，制备出TiC与TiB2等增强相增强钛基复合材料涂层。综合运用XRD、SEM、EPMA和TEM等分析手段研究了优化熔覆工艺条件下的NiCrBSi＋B4C激光熔覆层的组织结构与相组成，并对复合涂层进行了硬度测试，结果表明：NiCrBSi＋2％B4C熔覆层的微观组织是在γ—Ni和Ni3Ti＋Ni3B共晶的基体上均匀分布着TiB2、TiC、CrB等相的多元组织，激光熔覆层的硬度比Ti6Al4V基体硬度提高到3～4倍。     

Spark plasma sintering of B4C ceramics: The effects of milling medium and TiB2 addition

Boron carbide (B₄C) ceramics, with a relative density up to 98.4% and limited grain growth, were prepared at 1600-1800 °C by spark plasma sintering (SPS) technique. The effects of powder milling medium (water and 2-propanol) on the powders' surface characteristics and TiB₂ addition on the sintering densification were investigated. The ball milling processing of B₄C powders in water can promote the sintering of B₄C ceramics. A B₂O₃ layer on B₄C particle surface is concluded to promote the densification of the B₄C ceramics at an early sintering stage. This B₂O₃ layer, which normally inhibits the densification process at the final stage of the sintering, can be reduced through reaction with TiB₂ particles, resulting in further densification of the B₄C ceramics.     

Effect of air annealing on mechanical properties and structure of amorphous B4C films

Amorphous B₄C films were prepared by magnetron sputtering of the hot-pressed B₄C target in different regimes. Hardness, intrinsic stress and film structure were investigated in dependence on the annealing temperature in air.Changes in the film structure and composition were investigated by Raman spectroscopy, confocal microscopy, and electron probe microanalysis. It has been shown that an annealing at 500 °C for 1 h leads to stress reduction, slight thickness decrease and increase of film hardness. However already at 600 °C the film oxidation proceeds very intensively with formation of the phases of boron oxide and amorphous carbon in the surface layer. The thickness of the film decreases quickly.The film oxidation is accompanied by formation of numerous carbon hillocks and redistribution of film material after annealing in furnace at 500 and especially 600 °C. The oxidation of a-B₄C films as well as of the crystalline bulk samples starts in some locations and has clearly pronounced heterogeneous character that indicates heterogeneous structure of amorphous films as well as of bulk crystalline samples.Annealing in air for a long period shifts down the onset of formation of hillocks to 400 °C and changes in film morphology to 300 °C. Thus the upper temperature limit for application of a-B₄C films in air depends also on the exposure time at the operation temperature.     

SiC_f/Ti6Al4V/Cu复合材料的界面行为及力学性能

采用箔-纤维-箔法制备SiC_f/Ti6Al4V/Cu复合材料,研究Ti6Al4V在连续SiC纤维增强Cu基复合材料中作界面改性涂层时的界面反应结合特征.利用光学显微镜、扫描电镜和能谱仪分析复合材料显微组织、断口形貌以及SiC_f/Ti6Al4V界面和Ti6A14WCu界面的反应扩散特征.结果表明:该复合材料的抗拉强度并没有显著提高;SiC_f/Ti6Al4V界面反应非常微弱;而Ti6Al4V/Cu界面反应非常明显,主要是Ti原子与Cu原子之间的反应,反应层厚度约为20 μm;反应产物主要呈4层分布,分别为CuTi_2、CuTi、Cu_4Ti_3和Cu_4Ti.     

Ti6Al4V钛合金表面Al2O3颗粒改性微弧氧化涂层制备及性能

微弧氧化技术是一门新的表面处理技术,在很多领域有着广泛的应用前景,但其结构受限于电解液成分。本文通过在磷酸盐电解液中加入Al2O3陶瓷颗粒,使得在Ti6Al4V钛合金表面的微弧氧化涂层结构和性能得到改性。涂层的结构和性能通过扫描电镜和XRD衍射仪进行表征和测试,涂层的抗高温氧化性能和热震性能通过高温热循环氧化试验和热震试验进行测试。结果表明,通过在电解液中添加Al2O3陶瓷颗粒,涂层由Al2TiO5 and TiO2组成,涂层更为致密,表现出更为优异的抗高温氧化和热震性能。电解液中游动的Al2O3陶瓷颗粒在微弧氧化过程中被吸入到样品表面并进入涂层,涂层的结构和性能得到改性。     

B4Cp/6061Al复合材料动态再结晶临界条件

通过等温热压缩实验对25vol.% B₄C_p/6061Al复合材料的热变形行为和动态再结晶临界条件进行了研究,采用的温度范围为350℃-500℃,应变速率范围为0.001s_-1-1s_-1。应力-应变曲线显示动态再结晶是复合材料热变形过程中主要的软化机制,并利用峰值应力构建了基于Arrhenius形式的本构方程。基于加工硬化率曲线,求解了表示动态再结晶发生的临界应变与临界应力值。结果表明,临界应力与峰值应力存在线性关系：σ_c=0.8374σ_p-0.33708。此外,引入Zener-Hollomon 参数描述变形条件对临界条件的影响,得到临界应变与Z参数的关系：ε_c=2.39×10_-4Z_0.11022。最后,通过θ-ε曲线得到了复合材料完成动态再结晶时的稳态应变,并绘制了动态再结晶图。     

Microstructure and mechanical properties of B4C reinforced Al-based matrix composite coatings deposited by CGDS and PGDS processes

Coatings of a composite material consisting of an Al-12Si matrix reinforced with 20 wt.% B₄C particles were produced using Cold Gas Dynamic Spray (CGDS) and Pulsed Gas Dynamic Spray (PGDS) processes onto Al-6061 and SS-316L substrates. Two types of composite feedstock powders (mechanically mixed and cryomilled) were used. The influence of the coating process as well as the nature of the feedstock material on the coating microstructure and mechanical properties was studied. The combination of cryomilling to synthesize the feedstock powder and the spray processes provides a unique opportunity to produce hard and dense composite coatings with good cohesion between the deformed particles and good adhesion to the substrate, no phase degradation, very low compressive stresses and high dry sliding wear resistance. The two spray processes have shown almost similar results regarding microstructure and mechanical properties. No effect of the substrate material, Al-6061 and SS-316L, on the coating microstructure and properties was observed.     

Chemical kinetic studies on interfacial reaction in SCS-6 SiC/Ti matrix composites

Interfacial reaction and its mechanism of SiC/Ti composite were revealed by chemical kinetic studies. A two-step dynamic model of interfacial reaction in SCS-6 SiC/Ti composites was built up, and the rate constant and the activation energy of the interfacial reactions were obtained based on the quantum chemistry calculation. The results show that the first step, in which the atomic Ti, C and Si are decomposed from Ti matrix and SiC fiber, respectively, is a rate-determined step because the activation energy of the step is much larger than that of the second one in which deferent interfacial reaction products form. The theoretically predicted result of the interfacial reaction is coincident with that of experimental observation.