基于遗传算法的TC21钛合金高速车削工艺优化研究

通过TC21钛合金车削正交实验,测量表面粗糙度,基于响应曲面原理建立表面粗糙度预测模型,并以最大材料去除率为优化目标,采用遗传算法对不同表面粗糙度下的TC21钛合金高速车削参数进行优化,以期对生产实践起到一定的指导作用。     

钛合金深孔刀具耐用度及参数优化

深孔钻削钛合金难度大,刀具极易损坏。本文在原来自行设计和制造的内排屑钻孔（BTA）深孔钻头基础上．通过对钛合金材料的深孔加工试验,对改进后的深孔钻头的失效机理进行了分析研究,并探讨了钛合金深孔加工时进给量、刀具转速与耐用度的关系,优化了工艺参数和刀具结构、最终达到提高刀具耐用度的目的。     

大厚度TC21钛合金电子束焊接试验

对56mm厚TC21钛合金进行了电子束对接试验,对接头显微组织和力学性能进行了研究.结果表明,接头焊缝区组织形态以柱状β晶粒为基体,针状的马氏体弥散其中;热影响区从焊缝到母材分为三个区域,依次为等轴再结晶β晶粒区、片状和针状а相形成的魏氏组织区以及片状α相聚集长大的区域;熔合区内柱状晶与等轴晶联生.接头强度达到母材水平,断裂发生在母材内,接头厚度方向性能一致.接头塑性损失较大,只达到母材的50%左右.接头焊缝区硬度最高,其次是热影响区的等轴晶区和魏氏组织区,而热影响区内片状α相聚集长大的区域硬度值最低.

Abstract：

Electron beam welding of TC21 56 mm titanium alloy was carried out. The microstructure and the mechanical properties of welded joints were analyzed and tested. The results showed that the weld zone consisted of the columnar β gains, and in which the transgranular acicular α' martensite were dispersedly distributed. HAZ can be divided into three parts from base metal to weld zone, which are the equiaxed recrystallized β grain zone, Widmanstaten structure zone formed by lamellar and aeicular α phases and lamellar a phase coarsening zone. Fusion zone consists of the adnate columnar and equiaxed grains. Tensile strength of joints reaches to that of base metal and the failure appears in the base metal. The mechanical properties are uniform along the vertical direction. Plasticity in the welded joint is greatly decreased and only up to 50% of that of the base metal. The microhardness in weld zone is the highest, and that of the equiaxed grain zone and Widmanstaten structure zone in HAZ is higher, and the microhardness in columnar a phase coarsening zone is the lowest.     

损伤容限型TC21钛合金切削加工工艺研究概述

为克服TC21钛合金切削加工难题,促进其在航空领域的应用,中航飞机股份有限公司西安飞机分公司开展了TC21钛合金的各种机械加工工艺研究。介绍了该项研究所取得的成果,给出了TC21钛合金的锯切、车削、镗削、铣削、钻削、铰削、磨削与攻丝等各种切削加工方法的刀具选择方案和工艺参数,供同行业技术人员借鉴和参考。     

TC21钛合金表面处理技术的研究现状

介绍了TC21钛合金的表面处理技术,综述了阳极化处理技术、MAO、渗铬、渗碳、渗硼等耐磨技术以及喷丸处理技术和提高微动磨损性能的超音速火焰喷涂技术,展望了TC21钛合金表面处理技术的发展.     

新型TC21钛合金相变行为和相组成研究

采用X射线衍射(XRD)对TC21钛合金β热处理后,经不同冷却速率冷却及双重退火后的相结构进行了分析,并用扫描电镜(SEM)和透射电镜(TEM)对显微组织和相的形貌特征进行了观察研究。结果得出,TC21钛合金在β处理时经炉冷和水冷后,合金由α和β两相组成。空冷状态下,合金主相为α β,并有少量Nb3Si相析出。实验证明,冷却速率主要影响α和β相含量的比例,相的组成基本不受冷却速率的影响。合金经970°,30min,空冷 600℃,4h退火后,仍由α相和β相组成,没有发现新的析出相,但观察到转变β相中存在次生析出的细小针状α相。     

去应力退火对TC18和TC21钛合金吸氢含量的影响

在井式空气炉内按GJB 3763A—2004标准的最高温度和最长保温时间对TC18和TC21钛合金进行了去应力退火,研究了空气炉去应力退火对TC18和TC21钛合金吸氢含量的影响。结果表明:与去应力退火前相比,TC18钛合金经空气炉去应力退火后氢含量有所增加,而TC21钛合金氢含量反而降低。经去应力退火后,TC18和TC21钛合金的氢含量分别为0.0029%和0.0025%,远小于材料规范要求的氢含量(＜0.015%);随表层至中心(深度变化),氢含量未见明显的规律性变化,里层氢含量与表层氢含量相差不大。从吸氢量考虑,该两种钛合金均可采用空气炉进行消除应力热处理。     

TC21钛合金的全片层组织和冲击性能研究

利用光学显微镜、场发射扫描电镜和示波冲击试验机等研究了TC21钛合金在不同退火温度下的全片层组织演化规律和冲击韧性。结果表明：TC21钛合金经980 ℃固溶处理后,再经720、770、820 ℃退火处理,均能获得具有多层次特征的全片层组织。随着退火温度升高,TC21钛合金组织中α片层厚度、晶界α相厚度、α丛域尺寸都增大,而β晶粒尺寸基本保持不变。合金显微组织中小角度界面的比例随退火温度的升高而逐渐增加,冲击断裂过程中的裂纹形成功和扩展功也逐渐增大,且扩展功所占比例提高;断裂机制从穿晶断裂为主逐渐向沿晶界和丛域界断裂为主转变。     

热变形过程中TC21钛合金的微观组织演变

研究了TC21钛合金在不同应变速率和变形温度下的微观组织变化。结果表明,应变速率相对较低或者变形温度相对较低时,TC21钛合金才可以发生再结晶现象。     

TC21钛合金微弧氧化涂层微动磨损行为研究

采用球盘接触形式,在50 μm和150 μm位移振幅条件下,研究了载荷(60 N、40 N和20 N)对TC21钛合金及其表面微弧氧化(PEO)涂层切向微动磨损性能的影响。结果显示,随着位移振幅的增大和载荷的减小,TC21钛合金和PEO涂层的微动区域均由部分滑移区向滑移区转变。在部分滑移区,两种材料沿微动方向的磨痕宽度随载荷的减小而减小。虽均未出现明显的材料损失,但TC21钛合金边缘微滑区存在微裂纹的萌生和扩展,其程度随载荷的减小而加重,而微动对PEO涂层只起到了平滑作用。在滑移区,两种材料的磨痕宽度随载荷的减小而增大,且均存在局部磨损。磨损程度随振幅的增大和载荷的减小而加深。其中,PEO涂层的最大磨痕深度小于TC21钛合金,显示出更好的抗微动磨损性能。     

基于切削速度和高压润滑的钛合金切削磨损研究

介绍了在传统切削和高压喷射辅助切削方式下WC/Co硬质合金刀具对钛合金Ti17的加工,并进行了对比分析。在不同的切削速度和喷射压力下,研究了刀具的磨损演化以及切削力和轴向力的变化,并进行了相应讨论。在切削速度为50～100 m/min和喷射压力为5～25 MPa之间进行试验,确定了最佳润滑喷射压力和切削速度。当喷射压力为10 MPa时,最佳切削速度v_c为81.40 m/min,与常规润滑方式相比,刀具寿命提高约9倍,效率可提高约30%。     

高强高韧损伤容限型钛合金TC21研制

介绍了西北有色金属研究院新研制的高强高韧损伤容限钛合金TC21的情况。合金经实验室、中试及工业规模3个周期的深入研究,其各种力学性能稳定,具有良好的强度、塑性、断裂韧性、裂纹扩展速率的匹配,是1种非常有应用前景的高强高韧损伤容限型结构钛合金。     

TC4钛合金膝关节胫骨平台锻造防护润滑技术研究

介绍了玻璃基锻造用防护润滑剂的技术参数要求、设计原则和FR系列防护润滑剂,研究了适用于TC4钛合金人工膝关节胫骨平台锻造的玻璃基防护润滑剂的组分配比、性能及涂敷厚度,解决了TC4钛合金人工膝关节胫骨平台锻造的防护润滑问题。     

多重退火超塑性压缩TC21钛合金显微组织演变

针对TC21钛合金进行超塑性压缩变形及多重退火热处理,研究其对合金显微组织演变的影响。结果表明,在两相区超塑性压缩变形,大变形区与自由变形区相比,α相转变为亚稳β相的数量更多;在β单相区变形,变形温度越高,β相晶粒尺寸越大。随后进行双重退火热处理,在相同变形条件下,析出的针状α相尺寸虽然随退火次数不断变大,但形成的网篮组织交织程度更高。最后进行三重退火,形成的网篮组织比双重退火更为细密,并且降低双重退火温度,可显著减小析出的针状α相尺寸。对比发现,随着超塑性变形温度升高,无论双重退火还是3重退火,析出的针状α相尺寸都不断变大,退火前变形温度对退火后组织状态有显著影响。     

New cooling approach and tool life improvement in cryogenic machining of titanium alloy Ti-6Al-4V

Titanium alloy Ti-6Al-4V, a difficult-to-machine material because of its extremely short tool life, has been a major subject for cryogenic machining research. However, the approaches reported in past publications are inherently flawed. This study reviews how the temperature affects Ti-6Al-4V properties, and compares different cryogenic cooling strategies. Based on these findings, a new economical cryogenic cooling approach is proposed. Using a minimum amount of liquid nitrogen (LN2), this innovation features a specially designed micro-nozzle. Formed between the chip breaker and the tool rake face, the nozzle lifts the chip and injects focused LN2 into the chip–tool interface at the point of highest temperature. As the nitrogen evaporates, a nitrogen cushion formed by evaporating nitrogen lowers the coefficient of friction between the chip and the tool. An auxiliary mini-nozzle that sprays LN2 onto the flank at the cutting edge further reduces the cutting temperature. The study finds that the combination of these two micro-nozzles provides the most effective cooling while using the lowest LN2 flow rate. Improving the position of the nozzle/chip breaker further enhances the performance. Our cryogenic machining tests show that tool life increases up to five times the state-of the-art emulsion cooling, outperforming other machining approaches.     

Static globularization and grain morphology evolution of α and β phases during annealing of hot-rolled TC21 titanium alloy

A lamellar-structure TC21 titanium alloy was hot-rolled and subsequently annealed at 820, 880 and 940 °C for 1 and 6 h, and the effects of annealing parameters on static globularization and morphology evolution of both α and β phases were studied. The results show that α globularization process is sluggish due to the limited boundary splitting at 820 °C. With increasing temperature to 880 °C, the accelerated boundary splitting and termination migration promote the α globularization. At 820 and 880 °C, the static recovery (SRV) and recrystallization (SRX) induce the grain refinement of interlamellar β phase. However, the excessively high temperature of 940 °C results in the coarsening of α grains due to the assistance of Ostwald ripening, and produces coarse β grains mainly due to the absence of SRX in interlamellar β phases. Conclusively, 880 °C is an appropriate annealing temperature to produce a homogeneous microstructure in which globularized α and refined β grains distribute homogeneously.