SUJ2轴承钢超声疲劳GBF内裂纹扩展规律

利用超声疲劳低-高应力两步变幅加载技术研究了JIS SUJ2高强轴承钢疲劳断口上GBF(granular bright facet)内裂纹萌生与扩展规律。结果表明,随外加应力幅增加GBF尺寸减小,固定应力幅下的GBF尺寸为恒定值,与夹杂物尺寸无关;且在固定应力幅下,N f∝A槡inc-8,疲劳寿命N f随着夹杂物尺寸的增加而降低。研究表明,GBF形成于疲劳初期(在105周次左右,相应于小于1%的总寿命),随循环周次的增加,GBF尺寸基本不增加,直至接近最终疲劳寿命时(超过90%总寿命)GBF裂纹快速扩展直到最终尺寸。     

机械轴承用SUJ2钢的裂纹扩展机制分析

研究了轴承用SUJ2钢断口处GBF(granular bright facet)裂纹的扩展机制。结果表明,当应力幅值增加时GBF尺寸下降,且当应力幅值不变时GBF尺寸也保持不变。当夹杂物的尺寸变大时其疲劳寿命Nf下降。在疲劳初期形成GBF,当循环次数增加时,GBF尺寸基本保持不变,直到最终的疲劳断裂。     

氢对TC4钛合金电子束焊接头疲劳断裂特性的影响

采用统计分析的方法研究了固溶氧对TC4钛合金电子束焊接头疲劳寿命的影响,并对接头试样的疲劳断裂位置和疲劳断口形貌进行了观察与分析.结果表明,氢显著降低了TC4钛合金试样的疲劳寿命,氢含量0.028％(质量分数)的钛合金的疲劳寿命仅为未充氢试样的一半,当氢含量增大到0.120％时,疲劳寿命降到了未充氢的五分之一.疲劳试样多数断于接头的热影响区,造成这一结果的主要原因是热影响区的组织不均匀性和氢含量相对较高.断口的形貌特征表明,氢促进了疲劳裂纹的萌生和增加了裂纹扩展的速度,导致钛合金电子束焊接头的疲劳寿命显著降低.     

中碳高强度弹簧钢NHS1超高周疲劳破坏行为

测试了中碳高强度弹簧钢NHS1的超高周(109 cyc)疲劳破坏行为,并利用FESEM对疲劳断口进行了观察.NHS1钢的S-N曲线呈台阶型,在109 cyc内疲劳极限消失.疲劳断口分析表明,在高应力幅区,实验钢的疲劳破坏主要起源于基体表面;而在低应力幅长寿命区,疲劳破坏主要起裂于试样内部的夹杂物,形成"鱼眼"型断裂.在夹杂物周围存在一个粗糙的粒状亮区(GBF).GBF区边界的应力场强度因子为3.6 MPa·m1/2,与疲劳寿命无关,该值与疲劳裂纹扩展的门槛值相等;"鱼眼"边界的应力场强度因子同样与疲劳寿命无关,约为10.6 MPa·m1/2.     

GCr15钢旋转弯曲超长寿命疲劳性能分析

轴承钢GCr15旋转弯曲超长寿命疲劳实验获得的应力-寿命(S-N)曲线数据分散性较大且呈连续下降趋势,不能用台阶下降的S-N曲线描述.断口分析表明,在高应力幅区疲劳破坏主要起始于试样表面的加工划痕或夹杂物;随着应力幅的降低,疲劳破坏主要起始于试样内部的夹杂物.内部破坏均带有鱼眼特征,大部分的内部夹杂物周围带有颗粒亮区(GBF区).夹杂物尺寸的较大分散程度和小尺寸夹杂物的簇集是引起GCr15钢疲劳寿命分散性较大的因素.使用推定的GBF区成长率能够定量分析夹杂物尺寸对疲劳寿命分散程度的影响.     

微量氢对电子束焊接TA15钛合金疲劳寿命的影响

对TA15钛合金电子束焊接试样进行充氢,研究了充氢对显微组织形态的影响,并对微量氢对TA15疲劳寿命影响进行考察。显微组织研究表明:充氢量低于0.105%(质量分数)时,氢以固溶态存在于合金中,并未形成氢化物。疲劳试验结果表明:随充氢量的增加,疲劳寿命大幅下降;这是由于微量氢的存在降低了TA15合金的韧性,固溶氢增加了疲劳裂纹的扩展速率,且氢通过影响裂纹尖端的性能加速疲劳裂纹扩展。焊缝区马氏体束呈团状结晶,且以团为单位统一变形,导致断口上呈团簇形态;且氢对马氏体团疲劳扩展中的行为有一定影响。     

氢对Ti-2Al-2.5Zr钛合金疲劳性能的影响

研究了4种含量的氢对Ti-2Al-2.5Zr钛合金疲劳性能的影响。结果表明，自然含氢量的材料具有最好的疲劳性能。而当疲劳载荷大于材料的屈服强度时，氢含量对疲劳寿命基本没有影响；低于屈服强度后，疲劳寿命随着氢含量的升高而和。认为固溶的原子氢导致驻留滑移带软化，裂纹萌生提前，造成在较大△σ时充氢试样的疲劳寿命降低；而材料中氢化物对驻留滑移带（PSB）的阻碍作用导致氢化物与基体分离 而成为裂纹源，是小△σ下疲劳寿命降低扩要原因。     

原奥氏体晶粒尺寸对低合金高强度系泊链钢氢脆敏感性的影响

通过预充氢拉伸和动态充氢拉伸两种试验研究3种不同温度淬火然后560 ℃回火试样中原奥氏体晶粒尺寸对一种低合金高强度系泊链钢的氢脆敏感性的影响。结果表明,电流密度＞1.0 mA/cm²时发生氢诱发裂纹而在发生屈服时就脆断,原奥氏体晶粒尺寸对预充氢拉伸与动态充氢拉伸的氢脆敏感性都没有影响。当电流密度＜1.0 mA/cm²时,发生应力诱发氢致滞后裂纹而断裂,在预充氢后拉伸时,原奥氏体晶粒尺寸对氢脆敏感性略有影响,氢脆敏感性随原奥氏体晶粒增大而略微增大;在动态充氢拉伸时,原奥氏体晶粒尺寸对氢脆敏感性基本没有影响。因此,原奥氏体晶粒尺寸对这种低合金高强度系泊链钢的氢脆敏感性作用不明显。     

氢对纯镍多晶体循环形变行为的影响

对充分退火的、晶粒尺寸约30—40μm的工业纯镍试样,分别在未充氢、电解充氢和充氢-驱氢情况下进行了恒应变幅对称拉-压低循环疲劳试验,应变幅范围从2.7×10~(-3)到4.9×10~(-3).记录了一定循环周数后的塑性滞后回线,由此测量了循环应力峰值σ_p,摩擦应力σ_F和反向应力σ_B实验表明,该镍试样充氢后,除疲劳至断裂的总寿命有明显降低外,循环硬化速率、达到饱和时的应力峰值σ_p和摩擦应力σ_F均有降低,并随应变幅的增加越趋明显,而反向应力σ_B则不因充氢而有明显变化.结合扫描电镜观察的结果进行了分析讨论.     

INFLUENCE OF HYDROGEN ON CYCLIC DEFORMATION BEHAVIOUR OF PURE Ni

对充分退火的、晶粒尺寸约30—40μm的工业纯镍试样,分别在未充氢、电解充氢和充氢-驱氢情况下进行了恒应变幅对称拉-压低循环疲劳试验,应变幅范围从2.7×10~(-3)到4.9×10~(-3).记录了一定循环周数后的塑性滞后回线,由此测量了循环应力峰值σ_p,摩擦应力σ_F和反向应力σ_B实验表明,该镍试样充氢后,除疲劳至断裂的总寿命有明显降低外,循环硬化速率、达到饱和时的应力峰值σ_p和摩擦应力σ_F均有降低,并随应变幅的增加越趋明显,而反向应力σ_B则不因充氢而有明显变化.结合扫描电镜观察的结果进行了分析讨论.     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.