硬质合金弯曲疲劳性能研究

制备5种不同WC晶粒度和粘结相含量牌号硬质合金试样,其中牌号A～D试样进行3点弯曲疲劳S-N曲线测试,试验表明硬质合金低周疲劳性能与横向断裂强度具有一致性,高粘结相含量试样在同应力疲劳循环次数波动性小于低粘结相含量硬质合金。对疲劳断裂试样进行断口形貌特征分析,低晶粒度和低粘结相硬质合金疲劳裂纹出现在WC晶粒聚集或粗大WC晶粒处,断口形貌特征与静态断口形貌特征相似,疲劳特征不明显。大晶粒度和高粘结相硬质合金疲劳特征明显,粘结相Co出现较多韧窝,表面出现疲劳条纹,随循环周次增加,疲劳条纹越窄,粘结相Co韧窝串联,无法维持对WC颗粒粘连,导致其碎裂和剥落。同一应力水平作用下,随循环周次的增加粘结相Co受到的塑性变形越大,韧窝特征越明显,WC晶粒破碎或剥落越严重,孔隙越多。另对牌号A和牌号E不同工艺制备的试样进行同一应力下疲劳性能对比试验,结果表明不同的制备工艺与处理工艺对硬质合金疲劳性能有较大影响,且与后续使用性能有较强的对应性。     

WC基硬质合金在碱性溶液中腐蚀行为的研究

本文以WC-Co、WC-Co-Ni-Cr硬质合金为研究对象,采用电化学极化曲线测试以及扫面电镜观察等试验手段,研究了两种合金在不同pH值的碱性溶液中的腐蚀行为。结果表明:在pH=13的NaOH溶液中,WC-Co和WC-Co-Ni-Cr合金腐蚀行为一致,都以WC的溶解析出为主,而在pH=10～11的Ca(OH)_2溶液中,两种合金各相的析出略有差别,WC-Co合金中粘结相Co析出略大于WC,而WC-Co-Ni-Cr合金相反。在pH=9～10的磨削液中,WC-Co和WC-Co-Ni-Cr合金的腐蚀行为完全不同,前者粘结相Co的溶解析出量远大于WC,后者粘结相析出量略小于WC。在pH=7～8的冷却水中,WC-Co合金中粘结相Co的溶解析出量略大于WC,而WC-Co-Ni-Cr合金中粘结相和WC的溶解量接近。在不同pH值的碱性溶液中,WC-Co-Ni-Cr合金的自腐蚀电位与溶液的pH值有关,pH值越高,自腐蚀电位越负;WC-Co合金的自腐蚀电位与pH值并不是简单的线性关系,与溶液的成分密切相关。     

7075铝合金FSW接头腐蚀疲劳性能及断裂特征

以7075-T6铝合金搅拌摩擦焊接头为研究对象,对其显微组织结构、3.5% NaCl(质量分数)溶液腐蚀疲劳寿命和腐蚀疲劳断裂特征进行了研究,分析了7075铝合金搅拌摩擦焊接头的腐蚀疲劳性能及断裂过程.结果表明,7075-T6铝合金搅拌摩擦焊接头腐蚀疲劳S-N曲线方程为lgN=5.845-0.014S,随着应力幅增大,腐蚀疲劳寿命大幅度降低;腐蚀疲劳裂纹起源于接头的热影响区,逐渐扩展最终断裂于接头的焊核区.腐蚀疲劳断口存在多个裂纹源,且受到应力集中作用的影响,裂纹源萌生于腐蚀坑处.高应力作用加剧了试样边角部分的腐蚀损伤,导致边角比平面位置腐蚀程度更严重.裂纹扩展区出现了明显的晶间断裂和疲劳辉纹;在腐蚀介质和交变载荷的共同作用下,裂纹扩展区腐蚀程度最重,晶界处产生了阳极溶解现象并产生了“冰糖块状”和“蚁巢状”的形貌特征;瞬断区产生了大量解理台阶和二次裂纹,为脆性断裂,在第二相粒子分布区域存在孔洞形貌特征.     

WC-Co-(Ni)-(Cr)硬质合金在中性溶液中的腐蚀行为

以WC粉、Co粉、Ni粉及Cr3C2粉为原料,采用粉末冶金方法制备了3组不同粘结相成分的WC-Co-(Ni)-(Cr)硬质合金,通过极化曲线测试和浸泡实验研究了3组合金在中性溶液中的腐蚀行为,并采用扫描电镜、能谱分析、X射线光电子能谱(XPS)和EBSD等手段对其腐蚀机理进行了探讨。结果表明,WC-Co和WC-Co-Cr硬质合金在中性溶液中主要发生粘结相Co的腐蚀,浸泡产生的腐蚀产物主要是Co(OH)2;添加Cr将提高WC-Co硬质合金在中性溶液中的耐腐蚀性能,这可能与Cr的添加明显降低了粘结相中密排六方Co的含量有关;同时添加Ni和Cr可进一步提高WC-Co合金在中性溶液中的耐腐蚀性能,在pH=7的Na2SO4溶液中浸泡480 h后,WC-Co-Ni-Cr合金发生很少量的腐蚀。     

WC-Co-(Ni)-(Cr)硬质合金在中性溶液中的腐蚀行为

以WC粉、Co粉、Ni粉及Cr_3C_2粉为原料,采用粉末冶金方法制备了3组不同粘结相成分的WC-Co-(Ni)-(Cr)硬质合金,通过极化曲线测试和浸泡实验研究了3组合金在中性溶液中的腐蚀行为,并采用扫描电镜、能谱分析、X射线光电子能谱(XPS)和EBSD等手段对其腐蚀机理进行了探讨。结果表明,WC-Co和WC-Co-Cr硬质合金在中性溶液中主要发生粘结相Co的腐蚀,浸泡产生的腐蚀产物主要是Co(OH)2;添加Cr将提高WC-Co硬质合金在中性溶液中的耐腐蚀性能,这可能与Cr的添加明显降低了粘结相中密排六方Co的含量有关;同时添加Ni和Cr可进一步提高WC-Co合金在中性溶液中的耐腐蚀性能,在pH=7的Na2SO4溶液中浸泡480 h后,WC-Co-Ni-Cr合金发生很少量的腐蚀。     

WC-Co硬质合金冲击疲劳行为的研究

利用实验室自制的调温、调频、调载冲击实验机对3种组织成分的WC-Co硬质合金进行了不同实验条件下的冲击疲劳试验,研究了组织成分及实验条件对硬质合金冲击疲劳寿命的影响;通过扫描电子显微镜(SEM)及透射电镜(TEM)重点分析了疲劳过程中硬质合金微观组织的变化。结果表明:硬质合金的冲击疲劳寿命随试验温度和冲击能量的升高而下降,且随着冲击能量和试验温度的提高其疲劳敏感性增大。WC-Co合金的冲击疲劳断裂主要是以WC/WC界面和粘结相开裂为主,裂纹沿WC/WC和WC/Co界面及在Co相中扩展。随冲击次数的增加WC中位错数量增多并相互缠结,同时Co相发生面心立方-堆垛层错-密排六方的马氏体转变。     

硬质合金冲击疲劳行为的研究

本文综述了国内外有关硬质合金冲击疲劳行为的研究进展,旨在认识和揭示硬质合金在反复冲击载荷作用下的失效和断裂机理。重点总结了实验室中常用的硬质合金冲击疲劳性能评价方法,包括应力法和能量法;从WC平均晶粒尺寸、粘结相种类及含量、C含量、合金元素(Cr、V、Ta等)、腐蚀介质等方面分析了微观结构和服役环境对硬质合金冲击疲劳性能的影响;从裂纹的萌生、扩展及断裂方面阐述了硬质合金的冲击疲劳断裂机理。服役条件下的硬质合金往往不是受到单一的冲击作用,而是多种因素(载荷、温度、腐蚀介质等)的联合作用,今后有必要开展这方面的研究;另外硬质合金在冲击过程中的组织演变机理还不清楚,研究者可借助更为先进的手段(例如透射电镜原位观察等)对硬质合金的微区进行研究;此外研究者可以在总结试验数据和规律的基础上构建理论及数学模型并借助计算机软件对硬质合金的冲击过程进行动态模拟。     

深冷处理对WC-Co硬质合金组织和性能的影响

对YG8和YG25两种WC-Co硬质合金不同时间深冷处理后的力学性能和疲劳性能进行了研究,利用X射线衍射方法分析了深冷前后合金的相变和残余应力变化,通过扫描电子显微镜（SEM）观察了材料的断口形貌和断裂方式。结果表明：深冷处理能有效提高了WC-Co硬质合金的硬度、强度、耐磨性和疲劳寿命。深冷处理时间是最主要的工艺参数,对YG8合金来说,2 h为深冷处理最佳工艺时间,而YG25则为8 h。其性能变化的主要原因是深冷处理导致硬质合金表面残余应力的变化和Co粘结相发生马氏体相变。     

硬质合金的静态疲劳研究进展

疲劳是导致硬质合金材料失效和断裂的主要原因,所以研究硬质合金的疲劳性能,对于提高硬质合金的使用性能具有重要的指导意义。疲劳失效机理众多,但研究硬质合金静态疲劳的文献却相对较少,本文简要的介绍了近年来国内外在硬质合金静疲劳领域的一些研究成果。首先从断口微观形貌、应力比R及频率和相应的裂纹扩展公式来进行对比,区分了循环断裂和静态断裂两种疲劳裂纹扩展模式。围绕最能影响硬质合金静疲劳性能的参数最大应力场强度因子Kmax,从材料微观形貌、应力比、温度、频率及其他环境因素分析和讨论影响硬质合金静态疲劳性能的工艺参数。以期让读者更清楚的了解了硬质合金的静态疲劳性能,为进一步认识硬质合金疲劳失效机理和评估材料抗疲劳特性提供一定的参考。     

硬质合金疲劳性能研究进展

疲劳是影响硬质合金服役性能的主要因素之一,认识硬质合金疲劳失效机理及改善疲劳性能是目前硬质合金研究的重要方向。本文介绍了国内外硬质合金疲劳性能的研究动态,综合叙述了硬质合金疲劳裂纹的萌生和扩展行为,疲劳裂纹通常萌生于孔隙、微裂纹、钴池、异常长大的WC晶粒等缺陷处,从应力比、温度、腐蚀环境、化学成分及微观组织等方面分析了各因素对疲劳裂纹扩展行为的影响。总结了改善硬质合金疲劳性能的主要方法,通过提高粘结相含量、增加WC平均晶粒尺寸、添加Ni、Cr元素、热处理等可以有效提高合金疲劳性能。硬质合金在服役过程中需要承受热疲劳、机械疲劳、腐蚀疲劳等多种疲劳,接近真实服役状态下的多重疲劳机制耦合作用的疲劳性能还有待深入研究,对硬质合金疲劳性能测试评价的方法和理论还需要进一步完善。     

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.     

新型的治疗阿尔茨海默氏症药物(1-二甲基磷酰基-2,2,2-三氯)-乙基-1-醇烟酸醋对体外神经细胞的作用

目的: 观察本实验室合成的一种治疗阿尔茨海默氏症(AD)的药物(1-二甲基磷酰基-2, 2, 2 -三氯)-乙基^-1-醇烟酸醋(NMF),对体外培养的皮层神经细胞活性的影响以及对海人藻酸(KA)所致的神经损伤的保护作用。方法: 采用体外培养皮层神经元的方法,解剖分离 15 d胚胎小鼠皮层神经细胞, 接种于 96孔板,48 h 后加药并培养 72 h,以 MIT 法 观察 NMF 对小鼠皮层神经细胞活性的影响;同时将接种于 24 孔板的细胞预先给予 NMF,d 3 时加或不加KA处理后,以台盼蓝染色鉴别并计数死、活细胞,可得出细胞的存活率。结果: NMF 明显促进胎鼠皮层神经元活性,其中 NMF1、0. 1、10nmol·L^-1促进神经元活性增殖率分别高达 34.7%、37.4%、36. 7%, NMF 明显促进正常胎鼠皮层神经元存活卒,与对照组比较,10nmol·L^-1 NMF 对皮层神经元的存活率分别提高 39.3%、73.5%。 NMF能显著 对抗 KA 所致的神经元损伤,与 KA 损伤组相比, NMF0.1、10、10nmol·L^-1对损伤皮层神经元的保护率分别为 77.30%、80.10%、84.15%。结论: NMF 明 显促进胎鼠皮层神经元的洁性、提高正常皮层神经元,的存活卒,并能有效地保护KA所致的神经元损伤,提示 NMF 是一种很有潜力的治疗 AD 的药物。     

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).     

Three-Dimensional Growth of Coherent Ferrite in Austenite: A Molecular Dynamics Study

Coherent second phase often exhibits anisotropic morphology with specifi c orientations with respect to both the second and the matrix phases. As a key feature of microstructure, the morphology of the coherent particles is essential for understanding the second-phase strengthening eff ect in various industrial alloys. This letter reports anisotropic growth of coherent ferrite from austenite matrix in pure iron based on molecular dynamics simulation. We found that the ferrite grain tends to grow into an elongated plate-like shape, independent of its initial confi guration. The fi nal shape of the ferrite is closely related to the misfi t between the two phases, with the longest direction and the broad facet of the plate being, respectively, consistent with the best matching direction and the best matching plane calculated via the Burgers vector content(BVC) method. The strain energy calculation in the framework of Eshelby's inclusion theory verifi es that the simulated orientation of the coherent ferrite is energetically favorable. It is anticipated that the BVC method will be applicable in analysis of anisotropic growth and morphology of coherent second phase in other phase transformation systems.     

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.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.