Characterization of carbon/carbon composite/Ti6Al4V joints brazed with graphene nanosheets strengthened AgCuTi filler

Carbon/carbon (C/C) composite and Ti6Al4V alloy (wt%) were successfully brazed with graphene nanosheets strengthened AgCuTi filler (AgCuTiG). Graphene nanosheets (GNSs) with low CTE and high strength were dispersed into AgCuTi filler by ball milling. The interfacial microstructure was systematically characterized by varieties of analytical means including transmission electron microscopy (TEM). Results show that typical interfacial microstructure of the joint brazed at 880 °C for 10 min is a layer structure consisting of (Ti6Al4V/diffusion layer/Ti2Cu + TiCu + Ti3Cu4 + TiCu4/GNSs + TiCu + TiC + Ag(s,s) + Cu(s,s)/TiC/C/C composite). The interfacial microstructure and mechanical properties of brazed joints changed significantly as temperature increased. High temperature promoted the growth of TiCu and TiC phases, which were attached to GNSs. Meanwhile, the diffusion layer and primary reaction layers thickened as temperature increased, while the thickness of brazing seam decreased. The maximum shear strength of 30.2 MPa was obtained for the joint brazed at 900 °C for 10 min. GNSs decreased the thickness of brittle reaction layers and promoted the formation of TiCu and TiC phases in brazing seam, which caused the strengthening effect and decreased the CTE mismatch of brazed joints. The fracture modes are also discussed in this paper.     

Interfacial reaction behavior and bonding mechanism between liquid Sn and ZrO2 ceramic exposed in ultrasonic waves

Ultrasound-assisted dipping of ZrO₂ ceramics into molten Sn solder was performed to realize the low-temperature joining of ZrO₂ ceramics in this study. Scanning electron microscopy with energy dispersive spectrometer, X-ray diffraction and X-ray photoelectron spectroscopy were employed to study the effects of ultrasonic vibration on the microstructure of Sn/ZrO₂ interface, and to elucidate the joining mechanism between Sn coating layer and ZrO₂ ceramic. Results showed that, after ultrasonically dipping in molten Sn for 1200 s, a pure Sn solder layer with a thickness of approximately 8–9 µm was coated on the ZrO₂ surface. The Sn coating layer exhibited excellent metallurgic bonding with ZrO₂ ceramic. A nano-sized ZrSnO₄ ternary phase, which was beneficial to the smooth transition of the lattice from Sn solder to ZrO₂ ceramic, was formed at the Sn/ZrO₂ interface. The formation of ZrSnO₄ interlayer was ascribed to the acoustic cavitation induced high-temperature reaction of Sn, O and ZrO₂ at the molten Sn/ZrO₂ ceramic interface. The tested average shear strength of ZrO₂/Sn/ZrO₂ joints was approximately 32 MPa, and the shearing failure mainly took place within the Sn solder layer.     

Effect of brazing parameters on microstructure and mechanical properties of Cf/SiC and Nb-1Zr joints brazed with Ti-Co-Nb filler alloy

Reliable brazing of carbon fiber reinforced SiC (C_f/SiC) composite to Nb-1Zr alloy was achieved by adopting a novel Ti45Co45Nb10 (at.%) filler alloy. The effects of brazing temperature (1270–1320 °C) and holding time (5–30 min) on the microstructure and mechanical properties of the joints were investigated. The results show that a continuous reaction layer (Ti,Nb)C was formed at the C_f/SiC/braze interface. A TiCo and Nb(s,s) eutectic structure was observed in the brazing seam, in which some CoNb₄Si phases were distributed. By increasing the brazing temperature or extending the holding time, the reaction layer became thicker and the amount of the CoNb₄Si increased. The optimized average shear strength of 242 MPa was obtained when the joints were brazed at 1280 °C for 10 min. The high temperature shear strength of the joints reached 202 MPa and 135 MPa at 800 °C and 1000 °C, respectively.     

冷却条件对超级钢焊接接头组织和性能的影响

400MPa级超级钢主要特征是高洁净度和超细晶粒组织。采用钨极氩弧焊对400MPa级超级钢施焊,并对其空冷和水冷两种冷却方式下的显微组织和力学性能进行分析。结果表明,空冷条件下焊接接头热影响区（HAZ）晶粒严重长大、强度下降,并出现软化区;焊接过程采用喷水冷却加快了冷却速度,有效抑制了焊接接头热影响区晶粒的长大,改善了接头组织,提高了贝氏体和低碳马氏体的含量,进而改善了接头的综合力学性能,满足实际焊接要求。     

钢表面激光熔覆原位合成TiN复合涂层

选用Ti机械球磨粉末在Q235钢基体表面进行激光熔覆,并实时通入氮气,使钛与氮气发生反应原位合成TiN涂层.运用SEM,XRD,EDS和BSE分析方法对激光熔覆层的组织及成分进行分析,并对熔覆层硬度、高温稳定性及耐腐蚀性进行测试.结果表明,涂层由TiN,TiO₂和铁组成,涂层与基体形成了冶金结合,熔覆区组织成球形颗粒状,而稀释区组织多为树枝晶和针状晶,机械球磨过程可起到细化涂层晶粒作用.同时激光熔覆涂层具有较高的硬度及高温稳定性,当激光功率为1 000 W,扫描速度为600 mm/min时,TiN复合涂层最高表面显微硬度为951.5MPa,涂层耐腐蚀性不佳主要是因为涂层中孔洞及疏松等缺陷导致.     

Fabrication and Microstructural Control of Nano-structured Bulk Steels： A Review

There exist strong interests of developing nano-grained steels because of the outstanding properties including high strength/weight ratio, wear resistance, excellent toughness, and favorable cellular activity. This article reviews the main fabrication process and microstructural control of nano-structured steels over the last decades. Severe plastic deformation is considered as an effective route of obtaining the nano-grained microstructures. The process of cold-rolling and annealing of martensitic steel is a viable method to obtain bulk nano-structured low carbon steel, while the final thickness of the cold-rolling plate is limited. According to the theoretical results of the thermal simulation studies, a novel alloy design combined with the rapid transformation and rolling process is proposed to successfully fabricate nano-grained high strength bulk steel. The refinement mechanisms are expected to be taking advantage of increase in the transformation nucleation sites and inhibiting the grain coarsening. Moreover, corresponding mechanical properties are summarized.     

表面镀铝对22MnB5 钢薄板焊接性的影响

在22MnB5 钢板表面浸镀铝,采用钨极氩弧焊的方法焊接浸铝钢板和裸钢板,通过?旌阜烨慕鹣嘈蚊埠筒舛ɡ於狭亚慷?研究了焊接热输入和表面镀铝对焊缝组织和拉伸性能的影响。结果表明:焊缝热影响区中的不完全淬火区组织由马氏体、铁素体等组成,是接头中的软化区,力学性能最低,断裂在此发生;热输入较低会引起未熔合等成形缺陷,过大则会使焊缝组织变得粗大,适宜的热输入在3800 J/ cm 左右;浸铝层的存在对焊接参数(即热输入)的选择有影响,但不影响焊接力学性能。     

热加工对复合板不锈钢表层晶间腐蚀的影响

对压力容器用低合金钢/不锈钢复合板在热加工后的晶间腐蚀行为进行研究,主要针对三种常用表层不锈钢304,321及316L热加工后的晶间腐蚀特性进行探讨。结果表明:表层不锈钢中,321钢存在少量阶梯组织,接近凹坑组织,过多的热处理工序会引起其晶间腐蚀,但程度上轻于316L钢;304钢为明显的晶间腐蚀类型,受热处理的影响较大,严格控制热加工工艺可使其晶间腐蚀的倾向相对最轻;316L钢热加工过程中的晶间腐蚀倾向最为严重,应尽量减少热处理。合金元素较多的钢种(321和316L)在敏化温度热处理后,晶间腐蚀特征改变不大;低碳不锈钢(304)经热处理后,晶间腐蚀所受影响较大。     

Ce 盐封孔对 SiCp/ Al 复合材料表面 Ni-P 镀层的影响

为提高SiCp/Al复合材料的耐腐蚀性能,先化学镀镍,再沉积稀土封孔,讨论了稀土溶液主盐Ce(NO3)3浓度和沉积时间对镍-稀土多层膜耐蚀性能的影响。结果表明:化学镀镍的SiCp/Al复合材料在室温下沉积稀土时,采用Ce(NO3)3含量1 g/L、成膜时间2 h的条件获得的多层膜耐蚀性最好,其腐蚀电位为-0.48mV,腐蚀电流密度为3.54×10-8A/cm2;稀土在膜层中以Ce的氧化物颗粒堆积状态存在,起到了封孔的作用;膜层中的镍磷合金呈多晶态,而稀土含量少,未能测出;稀土溶液浓度越高,沉积速度越快,而在相同浓度下,膜层厚度随着时间的延长而增加,越厚则膜层结合力越差。     

Effect of graphite intercalation compounds in the interfacial zone on the mechanical and thermal properties of unidirectional carbon fiber reinforced spodumene composite

The interface in unidirectional carbon-fiber-reinforced β-spodumene matrix composite (UD-Cf/β-spodumene) significantly affected the thermal conductivity characteristics and mechanical properties due to the presence of a multi-layer interface. The mechanical and thermal properties of UD-Cf/β-spodumene composites with and without a multi-layer interface have been studied. The measured thermal conductivities, flexural strength and fracture toughness of composites with a multi-layer interface were much better than those composites with a clear interface. Interfacial layers with a multi-layer morphology originated from the diffusion of lithium from the β-spodumene matrix to the surface of the carbon fiber, which led to the formation of graphite intercalation compounds. The mechanical properties and thermal conductivity of UD-Cf/β-spodumene hot pressed at 1350 and 1400 °C were enhanced due to the textured interfacial microstructure and high thermal conductivity of graphite intercalation compounds. The textured interface decomposed at 1450 °C, resulting in the formation of a “strong” interface. Inevitably, the mechanical properties and thermal conductivity decreased.