热变形对GH4169合金中NbC析出相尺寸形貌影响研究

通过Gleeble3500热模拟试验机进行热压缩试验并结合微观组织观察和统计分析，研究了热变形对GH4169合金中NbC颗粒尺寸形貌、分布特征的影响规律。研究表明压缩过程中的绝热效应会导致试样心部温度的进一步升高，从而为变形过程中的NbC回溶提供条件。NbC颗粒与基体在变形过程中形成的高位错密度区促进了元素的扩散，并加速了小曲率半径的尖角区域回溶和钝化。随变形量的增加NbC回溶趋势增加，其平均尺寸与体积分数均呈降低趋势。变形过程金属流动会促进NbC颗粒的位移，在70%的变形量下，NbC颗粒平均间距增加趋势显著高于30%和50%变形量试样。因此随变形量的增加，NbC颗粒有从链状→链条弯曲→链条方向改变→弥散分布的分布特征，促进基体中原链状NbC呈细小、弥散分布。研究结果为GH4169闪光焊接性能的提高提供了直接的参考。     

High temperature deformation behavior and microstructure evolution of wrought nickel-based superalloy GH4037 in solid and semi-solid states

Cylindrical samples of Ni-based GH4037 alloy were compressed at solid temperatures (1200, 1250 and 1300 °C) and semi-solid temperatures (1340, 1350, 1360, 1370 and 1380 °C) with different strain rates of 0.01, 0.1 and 1 s⁻¹. High temperature deformation behavior and microstructure evolution of GH4037 alloy were investigated. The results indicated that flow stress decreased rapidly at semi-solid temperatures compared to that at solid temperatures. Besides, the flow stress continued to increase after reaching the initial peak stress at semi-solid temperatures when the strain rate was 1 s⁻¹. With increasing the deformation temperature, the size of initial solid grains and recrystallized grains increased. At semi-solid temperatures, the grains were equiaxed, and liquid phase existed at the grain boundaries and inside the grains. Discontinuous dynamic recrystallization (DDRX) characterized by grain boundary bulging was the main nucleation mechanism for GH4037 alloy.     

Microstructure and mechanical properties of TiC nanoparticle-reinforced Mg−Zn−Ca matrix nanocomposites processed by combining multidirectional forging and extrusion

TiC nanoparticle-reinforced Mg−4Zn−0.5Ca matrix nanocomposites were processed by combining multidirectional forging (MDF) and extrusion (EX). The grain size of the nanocomposite after MDF+EX multi-step deformation was significantly decreased compared with that processed only by MDF. The average size of the recrystallized grains gradually increased after EX with increasing the number of MDF passes at 270 °C. However, the grain size significantly decreased by MDF processing at 310 °C. Both fine and coarse MgZn₂ phases appeared in the (MDF+EX)-processed nanocomposites, and their volume fractions gradually increased with increasing the number of MDF passes before EX. Ultrahigh tensile properties (yield strength of ~404 MPa, ultimate tensile strength of ~450.3 MPa and elongation of ~5.2 %) were obtained in the nanocomposite after three MDF passes at 310 °C followed by EX. This was attributed to the refinement of the recrystallized grains, together with the improved Orowan strengthening provided by the precipitated MgZn₂ particles that were generated by MDF+EX multi-step deformation.     

Unsteady conjugate mass transfer of a 2D deformable droplet in a modest extensional flow in across-slot

This work aims to investigate the unsteady conjugate interphase mass transfer between a stationary deformed drop and the modest extensional flow in a cross-intersected 2D channel. It is very difficult to accurately quantify the transient mass transfer rate of solute in such a geometry. Therefore, we established a mathematical model on the basic of the Stokes equation and solved it by the boundary element method, which could deal precisely with a two-phase flow system with a deformable interface; meanwhile, the convection-diffusion equation was solved by the finite difference method to calculate the unsteady conjugate interphase mass transfer. The simulation results showed that the mass transfer rate, analyzed and characterized in terms of mean concentration variation and Sherwood number Sh, was affected by capillary number Ca, Peclet number Pe, viscosity ratio λ , interior-to-exterior diffusivity ratio K, distribution coefficient m, and wall effect factor W.     

金属薄板平面铣削形变分析与控制

由于初始残余应力的作用,金属薄板平面加工普遍存在加工难度大,加工变形严重等问题,难以保证板面的加工质量。以不锈钢薄板的平面加工为基础,通过理论分析、仿真模拟和实验验证的方式,对金属薄板的加工形变进行较为系统的研究,分析了金属薄板加工形变的关键因素,总结了金属薄板残余应力分布形式以及有效避免加工形变的工艺方法,为类似金属板材加工提供理论参考依据。     

铁素体/贝氏体双相钢循环载荷作用下变形行为的模拟研究

为了避免铁素体/贝氏体双相钢管线管在服役过程中的交变载荷作用下引起的塑性损伤，采用有限元模拟方法，建立了Chaboche随动强化模型，研究了铁素体/贝氏体双相钢在循环应变载荷作用下的变形行为。结果显示，在循环应变作用下，应变优先在铁素体中形成累积，并在铁素体、贝氏体界面集中；随应变幅的增大，应变带在铁素体中形成，而贝氏体内累积应变增加不大，两相界面应变差增大。研究表明，铁素体内应变和两相应变差的增加将降低双相钢的塑性变形能力。     

热处理工艺对TC4钛合金冲击磨损性能的影响

研究了退火和固溶时效处理对热轧态TC4钛合金的力学性能和组织的影响,并考察了其冲击磨损性能。结果表明:退火处理后试样组织中转变β相增加,强度、塑性和韧性均较热轧态有所提升;而固溶时效处理后试样组织的晶粒细化且尺寸更为均匀,同时具有最高的强度,而塑性和韧性则较热轧态有所降低。经过10 h的冲击磨损试验后,退火态试样的磨损率最低,而固溶时效态试样的磨损率最高。通过磨损断口观察发现退火态试样表面冲刷犁沟较短,且终点处存在合金的塑性堆积,同时磨损面组织发生塑性变形,晶粒延展拉长。退火态试样较高的塑性和韧性有助于吸收冲击能量,因此表现出较好的耐冲击磨损性能。     

热变形工艺对含硫非调质钢流变应力及组织的影响

在变形温度950~1150 ℃和应变速率0.01~5 s^-1下,通过Gleeble-3500热模拟试验机进行单道次压缩试验,研究了热变形工艺对含硫非调质钢F45MnVS流变应力及组织的影响。结果表明:随着应变速率的增大,热压缩过程中的峰值应力增加,随着温度的升高,峰值应力降低;动态再结晶平均晶粒尺寸随着应变速率、变形量的增加而减小,随着温度的提高而增大。     

高温泵轴承失效分析及润滑可靠性监测系统的应用

某重油催化装置油浆泵采用集中油雾润滑方式,油液监测发现轴承润滑油中的金属元素含量高,并且呈急剧增加的趋势,拆机检查发现油浆泵轴承出现了严重磨损。分析该油浆泵轴承磨损原因,提出了采用稀油润滑和油雾润滑组合方式来改善轴承润滑。同时,采用了大型炼化企业机泵群油液监测平台对关键动设备进行状态监测,有效保证了设备长周期安全运行。