退火处理对激光沉积制造TC4钛合金组织及力学性能影响EI北大核心CSCD

以TC4球形粉末为原料,采用激光沉积制造技术制备TC4钛合金厚壁件。通过光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射(XRD)等方法研究了退火处理对激光沉积制造TC4显微组织及力学性能的影响。结果表明:试样经α+β两相区退火处理后,显微组织为网篮组织,经β单相区退火后,组织转变为魏氏组织;退火试样力学性能仍存在各向异性:Z向试样强度较低,塑性较好,而XY向试样强度高,塑性较差,退火温度对试样的各向异性具有明显影响;XY向试样拉伸性能存在较明显的分散性;α+β两相区退火处理后两个方向上均为韧性断裂,β单相区退火处理后试样强度与塑性大幅下降,且XY向试样为脆性断裂。     

Effect of welding speed on microstructures and mechanical properties of underwater friction stir welded 2219 aluminum alloy

Underwater friction stir welding (underwater FSW) has been demonstrated to be available for the strength improvement of normal FSW joints. In the present study, a 2219 aluminum alloy was underwater friction stir welded at a fixed rotation speed of 800 rpm and various welding speeds ranging from 50 to 200 mm/min in order to clarify the effect of welding speed on the performance of underwater friction stir welded joint. The results revealed that the precipitate deterioration in the thermal mechanically affected zone and the heat affected zone is weakened with the increase of welding speed, leading to a narrowing of softening region and an increase in lowest hardness value. Tensile strength firstly increases with the welding speed but dramatically decreases at the welding speed of 200 mm/min owing to the occurrence of groove defect. During tensile test, the joint welded at a lower welding speed is fractured in the heat affected zone on the retreating side. While at higher welding speed, the defect-free joint is fractured in the thermal mechanically affected zone on the advancing side.     

新型Ti-650合金电子束焊接头组织及性能研究

采用电子束对新型耐650 ℃使用的高温钛合金板材进行焊接,并进行1 000 ℃/1 h/AC+700 ℃/4 h/AC的退火处理,研究了接头的组织、硬度分布,母材和接头的拉伸性能和持久性能.结果表明,接头组织由α相、少量β相、以及大量细小的再结晶α相构成.接头中母材、热影响区和焊缝的显微硬度值比较均匀,介于440~490HV之间.室温条件下,母材和接头的抗拉强度均高于1 000 MPa,延伸率均介于7%~10%;650 ℃拉伸,母材抗拉强度达到了750 MPa,延伸率最高达20%;接头的抗拉强度在700 MPa以下,延伸率在10%~14%之间.接头与母材的持久断裂均是由孔洞聚集形成微裂纹,在力的作用下不断扩展,直至最终断裂.而接头中柱状晶的晶界促进了裂纹的扩展,所以母材的持久寿命和应变优于接头.根据结果分别得出了650 ℃下接头和母材应力与寿命的关系式.     

Effect of an electron beam surface treatment on the microstructure and mechanical properties of SAF 2205 joints produced with electron beam welding

The aim of present investigation is to study the effect of an electron beam surface treatment on 2205 duplex stainless steel joints produced by the same electron beam process. Heat treatment of the joints is necessary, to re-establish the ferrite/austenite balance, which is extremely disturbed during the electron beam welding process. For assessing the effectiveness of the electron beam surface treatment, similar weld joints were subjected to conventional furnace heat treatment at 1050 °C, and used as reference. Metallographic techniques and mechanical testing were used to assess the microstructure and corresponding mechanical properties of the as-welded and heat treated specimens. The metallographic results showed that an austenite/ferrite ratio approaching the one produced by a typical furnace post-weld heat treatment can also be achieved by heating locally the weld surface with an electron beam. At the same time the tensile properties show considerable improvement, approaching those obtained by means of a conventional furnace heat treatment, whereas the impact strength is also improved compared to the as welded specimen, but remains clearly lower than the one of the furnace heat treated weld.     

电子束快速成形TC4合金的组织与断裂性能

利用超景深显微镜和扫描电镜对电子束选区熔化快速成形的沉积态TC4试样组织与断口形貌进行观察和分析,研究不同几何成形和加载方向对断裂性能的影响。结果表明,断裂性能在垂直试样中受到柱状晶组织的影响,具有各向异性,在沉积方向上的断裂韧度为94.94MPa·m^1/2,大于电子束扫描方向的断裂韧度85.33MPa·m^1/2,而伸长率很小,仅为3%;α相形态对断裂性能有影响:水平试样片层状的α集束组织伸长率及断裂韧度优于垂直试样相互交错的针状α组织,最大值为14.5%和101.45MPa·m^1/2,而抗拉强度和屈服强度较小;电子束选区熔化制备的TC4试样断口由许多不同尺寸的韧窝和弯曲的撕裂棱组成,断裂方式以延性韧窝状沿晶断裂为主,水平试样的断口撕裂棱曲折程度、韧窝尺寸和深度大于垂直试样。     

Effect of pre- and post-weld heat treatments on the mechanical properties of electron beam welded Ti-6Al-4V alloy

This paper represents a summary of experimental work carried out to find the effect of various pre- and post-weld heat treatments on Ti-6Al-4V alloy. In the as-welded state the samples exhibit about 80% of the tensile ductility and about 90–95% of the impact/fracture toughness of the base metal. Low temperature stress relieving or ageing carried out subsequent to the welding operation improves the tensile properties but decreases the toughness at the fusion zone. Solution treatment followed by welding and ageing or the post-weld solution treatment and ageing treatment leads to only a marginal increase in tensile strength at the expense of toughness at the fusion zone. High temperature annealing of the welded samples does not increase the tensile ductility but improves the toughness at both the fusion zone and the heat affected zone. The above facts and a special burst-pressure test conducted on a gas bottle in the as-EB welded state show that Ti-6Al-4V components can be used without subjecting them to any post-weld heat treatments.     

医用酒精溶液对TC4钛合金力学性能的影响

在常温下对经医用酒精浸泡过的TC4钛合金试样进行单轴拉伸实验和超声疲劳实验,以研究医用酒精溶液对TC4钛合金力学性能的影响.单轴拉伸实验结果表明酒精对TC4钛合金的单轴拉伸力学性能影响极小,而经酒精浸泡再放置一段时间后,TC4钛合金的屈服强度有一定的变化.超声疲劳疲劳试验结果表明TC4钛合金经酒精浸泡后,其疲劳性能明显下降.酒精对TC4钛合金力学性能影响,是由于医用酒精降低了TC4钛合金内局部塑性,钛合金在酒精溶液中发生渗氢反应,使钛合金固溶氢浓度增加,在外载荷作用下,氢向材料缺陷处扩散富集,形成氢脆降低了材料局部塑性.     

Numerical investigation on the variation of welding stresses after material removal from a thick titanium alloy plate joined by electron beam welding

The stress modification after material removal from a 50 mm thick titanium alloy plate jointed by electron beam welding (EBW) was investigated through the finite element method (FEM). The welding experiment and milling process were carried out to experimentally determine the stresses induced by EBW and their modification after local material removal. The modification of as-welded stresses due to the local material removal method and the whole layer removal method was discussed with the finite element analysis. Investigated results showed that with less materials removal from the top, the stresses on the bottom surface remain almost unchanged; after material removal from the top and bottom part, the transverse stress on the newly-formed surface decreases significantly as compared to the as-welded stresses at the same locations; however, the stress modification only occurs at the material removal region in the case of local region removal method; the longitudinal stress decreases with the whole layer removal method while remains almost unchanged with the local region removal method.     

多重热处理对TC4合金的组织和力学性能的影响

研究了多重热处理对TC4钛合金的显微组织和力学性能的影响.多重热处理温度中第一重处理位于单相区,第二重位于两相区,前两重热处理均采用不同的冷却速率,最后进行时效处理.结果表明:采用不同多重热处理制度可以调节材料的显微组织参数,包括片状α的长度、宽度、长宽比以及次生α片层的数量等,从而可以优化材料力学性能的搭配,特别是显著提高片层组织的塑性.采用适当的多重热处理不仅提高了材料的强度和塑性,而且使材料的断裂韧性有一定程度的提高.     

碳对高温钛合金Ti-60组织和性能的影响

在Ti-60合金中碳的加入量大于0.17%时,组织中析出TiC结构的碳化物.在α β相区再结晶,碳偏聚于初生α(αp)相,导致碳化物主要在β转变组织中析出,其析出的百分数取决于αp体积分数.在β相区热处理,析出的碳化物钉扎β原始晶界,阻碍β晶粒的长大.β晶粒尺寸D、碳化物颗粒直径d和体积分数f三者遵循D/d∝f-1/3关系.随着碳含量的增加,β晶粒尺寸减小,α'片层通过界面迁移迅速长大以及形成α片层的合金元素的扩散速度加快,导致α'或α片层的厚度增加.碳的加入量小于0.09%时,碳完全固溶于基体中,产生固溶强化,β晶粒细小,导致合金的强度和蠕变抗力提高.碳含量增加导致粗大碳化物颗粒的析出,变形时产生应力集中使合金的塑性和蠕变性能降低.     

Effect of cerium on microstructures and mechanical properties of AZ61 wrought magnesium alloy

The effects of Cerium (Ce) addition on microstructures and mechanical properties of hot-extruded AZ61 alloy were investigated. It is found that Ce refines Mg₁₇Al₁₂ particles and brings about precipitation of a new rod-like phase that is identified as Al₄Ce by X-ray diffraction. During hot deformation, Al₄Ce particles can refine dynamic recrystallized grains by impeding grain growth. For Ce additions up to 1.0 wt%, the recrystallized grain size decreases; When Ce addition is more than 1.0 wt%, grain size increases inversely. Strength and elongation of extruded or annealed specimens at room temperature increase along with Ce addition up to 1.0 wt%, then decrease. Optimal mechanical properties are correspondent to 1.0 wt% Ce addition.     

Effect of interlayer addition on microstructure and mechanical properties of NiTi/stainless steel joint by electron beam welding

NiTi/Stainless Steel(SS) sheets have been welded via a vacuum electron beam welding process, with three methods(offsetting electron beam to SS side without interlayer, adding Ni interlayer and adding Fe Ni interlayer), to promote mechanical properties of the Ni Ti/SS joints. The joints with different interlayers are all fractured in the weld zone near the Ni Ti side, which is attributed to the enrichment of intermetallic compounds including Fe2 Ti and Ni3 Ti. The fracture mechanisms of different joints are strongly dependent on the types of interlayers, and the joints without interlayer, adding Ni interlayer and adding Fe Ni interlayer exhibit cleavage fracture, intergranular fracture and mixed fracture composed of cleavage and tearing ridge, respectively. Compared with the brittle laves phase Fe2 Ti, Ni3 Ti phase can exhibit certain plasticity, block the crack propagation and change the direction of crack propagation. The composite structure of Ni3 Ti and Fe2 Ti will be formed when the Fe Ni alloy is taken as the interlayer, which provides the joint excellent mechanical properties, with rupture strength of 343 MPa.     

Effect of electromagnetic stirring on the microstructures and mechanical properties of magnesium alloy resistance spot weld

This paper investigates the effect of electromagnetic stirring (EMS) on the nugget formation, microstructure, and mechanical properties of magnesium alloy resistance spot weld (RSW). The EMS was induced by an external magnetic field (EMF), which produced by a pair of permanent magnets. The results showed that the EMS drove the molten metal in the nugget to flow clockwise and generated a centrifugal movement, which brought high temperature molten metal from the center of the growing nugget to its edge. Compared with the traditional magnesium alloy RSW, the weld under the EMS effect (EMS-RSW) exhibited larger weld diameter, higher tensile shear force and energy absorption, and finer equiaxed crystal and columnar crystal. The EMS-RSW had a higher hardness ratio of fusion zone to pullout failure location, which indicated that the EMS-RSW was more sensitivity to experience pullout failure. Finally, an empirical failure load formula for magnesium alloy resistance spot weld was developed.     

热处理对TC4-DT钛合金组织性能的影响

研究了Ф300mm的TC4-DT钛合金几种热处理工艺参数对显微组织和室温性能的影响。研究表明α＋β区锻造Ф300mm的棒材晶粒较大,低倍呈现模糊晶,局部区域有明显的清晰晶,表明大规格棒材锻造均匀性较差。大规格的棒材＋双重退火热处理后,拉伸性能和断裂韧性均能达到Rm≥825MPa,RP0.2≥750MPa,A（纵向）≥8％,Z≥15％;KIC（T—L）≥90MPa·m1/2,具有良好的强度塑性匹配性能。α＋β相区锻造的Ф300mm棒材经965℃／1h Ac十550℃／6h AC和940℃／1h AC＋570℃／6h AC处理后,疲劳裂纹扩展速率在△K=11MPa·m1/2时,分别达到2．833036×10^-6mm／cycle和7．294209×10^-6mm／cyele。     

少量Sc对7055铝合金组织与性能的影响

利用拉伸试验、光学金相、X射线物相分析、SEM及TEM等实验方法,研究了添加0.2%Sc(质量分数)对7055铝合金组织与性能的影响.实验结果表明,添加0.2%Sc可以显著细化7055铝合金铸态晶粒并减少晶界非平衡共晶相数量,促进非平衡共晶相在均匀化退火时的溶解,从而提高合金固溶度;由于Sc的添加可以提高7055Sc合金的溶质原子固溶度、形成更为均匀弥散分布的Al3ScZr粒子、以及抑制变形组织再结晶和有效细化固溶处理后的(亚)晶粒尺寸,因而显著提高7055Sc合金综合力学性能.     

低温对时效态TC4合金拉伸性能的影响

在77－300K温度范围内对不同时6效状态TC4合金进行拉伸试验，研究了低温对时效态合金拉伸性能的影响。时效温度取813天，时效时间分别为0．5h、7h、60h。试验结果表明：在室温下，时效0．5h合金与退火态合金相比强度明显提高，延伸率略有降低；时效时间大于0．5h，随时效时间的延长，合金的强度与延伸率均下降。随试验温度的降低，3种时效态合金的强度都单调增加，延伸率先是下降，但在77K时又略有升高，TEM观察表明，随着试验温度的降低，拉伸断口附近位错分布不均匀性增大。     

Effect of temperature on deformation behavior and microstructures of TC11 titanium alloy

The isothermal compression deformation behavior of TC11 titanium alloy with beta microstructure was studied between 750 °C and 1100 °C under the strain rate ranging from 0.001 s⁻¹ to 10 s⁻¹ by THERMECMASTOR-Z simulator. In addition, the effect of temperature on microstructure was observed using optical microscope. The results showed that the temperature greatly affected the flow stress and microstructure of TC11 titanium alloy cooled from beta phase region in air. During hot deformation of TC11 titanium alloy, the steady state flow characteristic was observed at higher temperature or lower strain rate. In the α + β phase region, spheroidization fraction of α lamellar decreased with increasing temperature, while in near-β and β phase regions, dynamic recrystallization fraction increased with increasing temperature in all strain rates except at the strain rate of 0.001 s⁻¹.     

Reasons for superior mechanical and corrosion properties of 2219 aluminum alloy electron beam welds

Electron beam welds of aluminum alloy 2219 offer much higher strength compared to gas tungsten arc welds of the same alloy and the reasons for this have not been fully explored. In this study both types of welds were made and mechanical properties were evaluated by tensile testing and pitting corrosion resistance by potentio dynamic polarization tests. It is shown that electron beam welds exhibit superior mechanical and corrosion properties. The weld metals have been characterized by scanning electron microscopy; transmission electron microscopy and electron probe micro analysis. Presence of partially disintegrated precipitates in the weld metal, finer micro porosity and uniform distribution of copper in the matrix were found to be the reasons for superior properties of electron beam welds apart from the fine equiaxed grain structure. Transmission electron micrographs of the heat affected zones revealed the precipitate disintegration and over aging in gas tungsten arc welds.     

TC4-DT合金的超塑性变形及其本构方程

采用CMT4104电子万能拉伸试验机分别进行温度为870℃,应变速率为3.3×10-4s-1的恒应变速率和温度为850~890℃,应变速率为3.3×10-5~3.3×10-3s-1的应变速率循环法超塑性拉伸实验。结果表明:在变形过程中存在动态回复与动态再结晶现象,并采用Avrami方程描述了动态再结晶动力学行为;基于应变速率循环法获得了TC4-DT合金的本构模型,再通过1stopt软件加以回归拟合,得到较为精确的TC4-DT合金超塑性变形本构方程。