送粉角度对激光熔覆铁基复合涂层形状特征的影响

通过分析激光熔覆过程中光束、粉末和熔池间的作用机理,建立了送粉式激光熔覆材料有效利用率的数学模型,在此基础上推导了送粉角度与工艺参数之间的定量关系式,并计算了不同送粉角度下的熔覆材料有效利用率、熔高和横截面积。结果表明,在熔覆工艺参数不变的条件下,理论计算的熔覆材料有效利用率、熔覆层高度和横截面积均随送粉角度的增加而增大,且均高于实验检测值。激光熔覆过程中,由于粉末烧损和机械损失,使熔覆材料有效利用率、熔高和横截面积随送粉角度变化出现最大值,理想送粉角度为60。     

等温淬火热处理工艺对Fe-0.5C-2.0Si-2.5Mn钢冲击磨损性能的影响

采用MLD10动载磨粒磨损试验机对成分为Fe-0.5C-2.0Si-2.5Mn的贝氏体/马氏体复相钢进行冲击磨损试验,通过观察磨损率,表层组织演变以及表面磨损形貌的变化过程,重点研究了等温淬火热处理工艺对Fe-0.5C-2.0Si-2.5Mn钢冲击磨损性能的影响,结果表明:经不同热处理后的贝氏体/马氏体复相钢的耐磨性较铸态有明显提高(1.4~2.3倍),随着下贝氏体含量的增加,耐磨性先降低再趋于平稳.当冲击功由1 J增至4 J时,材料磨损性能下降,表面磨损形貌表征塑形破坏加剧;当冲击功为5 J时,组织中出现大量形变马氏体,加工硬化明显,表面磨损形貌较低能冲击下的表面更为平整均匀,磨损性能增强,但出现强烈的脆性断裂倾向.     

磁场辅助激光熔覆制备Ni60CuMoW复合涂层

采用磁场辅助激光熔覆技术,在Q235钢表面制备了Ni60CuMoW复合涂层,借助SEM,EDS 和XRD 等表征手段对涂层进行了微观组织和物相分析,利用维氏硬度计测试了复合涂层截面的显微硬度分布,通过摩擦磨损实验和电化学测试系统研究了复合涂层的磨损性能和耐腐蚀性能。研究结果表明:涂层主要由-Ni,Cu）固溶体、硅化物和硼化物组成,Cr3Si晶粒细化且均匀致密;磁场辅助作用下,激光熔覆涂层平均显微硬度达到913HV0.5,为无磁场辅助涂层的1.5 倍,磨损失重仅为无磁场涂层的36%,自腐蚀电位上升了100 mV,腐蚀电流密度降低了70%,耐磨耐蚀性能得到了显著改善。     

Stability and elastic properties of Nb_xC_y compounds

Density functional theory(DFT) is applied to investigate the stability and mechanical properties of NbxCy compounds.The structures of NbxCy compounds are optimized, and the results are in good agreement with previous work. The calculated results of the cohesive energy and the formation enthalpy of NbxCy show that they are thermodynamically stable structures, except for Pmc21-Nb2 C. The mechanical properties such as the bulk modulus, Young’s modulus, the shear modulus, and Poisson’s ratio are obtained by Voigt–Reuss–Hill approximation. The results show that the Young’s modulus and shear modulus of NbC are larger than other NbxCy compounds. The mechanical anisotropy is characterized by calculating several different anisotropic indexes and factors, such as universal anisotropic index(AU), shear anisotropic factors(A1, A2,A3), and percent anisotropy(ABand AG). The surface constructions of bulk and Young’s moduli are illustrated to indicate the mechanical anisotropy. The hardness of NbxCy compounds is also discussed in this paper. The estimated hardness for all NbxCy compounds is less than 20 GPa.     

交变磁场对激光熔覆Fe基复合涂层组织结构及其耐磨性的影响

采用激光熔覆辅助电磁控制工艺在45钢表面合成了Fe-Cr-Si-B-C复合涂层.通过对熔覆层进行SEM、EDS和XRD表征,研究了外加交变磁场对涂层微观组织和物相结构的影响.结果表明:外加磁场可降低激光熔池固-液界面前沿液相的温度梯度和增加非均质形核率,促使粗大、方向性很强的柱状晶转变为均匀、细小的等轴晶,并能够消除熔覆层内的气孔和裂纹等缺陷,但其对熔覆层物相组成的影响不大.熔覆涂层由白色初生γ-(Fe,Cr)固溶体相和其间黑色的γ-(Fe,Cr)共晶相组成,同时含有少量Fe3(B,C)、Cr7(B,C)3、CrFeB等碳化物和硼化物.常温干摩擦磨损试验表明,外加磁场所制备的涂层耐磨性能得到明显提高,其磨损失重仅为未加磁场的43％,且摩擦系数波动较小.     

规则多孔铜基自润滑材料的干摩擦磨损性能

采用液态金属浸渗法制备了以规则多孔铜为基体,纯铅为润滑相的新型自润滑材料,利用MMU-5G高温端面摩擦磨损试验机测试了新型自润滑材料在不同载荷下的摩擦系数与磨损率,并借助SEM、EDS、XRD等表征手段分析了新型自润滑材料试样在不同载荷下的摩擦磨损机理.结果表明:新型自润滑材料的整体摩擦磨损性能优于同等铅含量的铸造铜铅合金;新型自润滑材料在载荷大于200 N时,摩擦系数小于0.08,磨损率仅为铸造铜铅合金的1/10～1/5;增大铅含量,能够进一步降低摩擦系数;随着试验载荷的增加,磨损机制从磨粒磨损转变为塑性变形和粘附作用.     

Stability,electronic structures,and mechanical properties of Fe–Mn–Al system from first-principles calculations

The stability, electronic structures, and mechanical properties of the Fe–Mn–Al system were determined by firstprinciples calculations. The formation enthalpy and cohesive energy of these Fe–Mn–Al alloys are negative and show that the alloys are thermodynamically stable. Fe_3Al, with the lowest formation enthalpy, is the most stable compound in the Fe–Mn–Al system. The partial density of states, total density of states, and electron density distribution maps of the Fe–Mn–Al alloys were analyzed. The bonding characteristics of these Fe–Mn–Al alloys are mainly combinations of covalent bonding and metallic bonds. The stress-strain method and Voigt–Reuss–Hill approximation were used to calculate the elastic constants and moduli, respectively. Fe_(2.5)Mn_(0.5)Al has the highest bulk modulus, 234.5 GPa. Fe_(1.5)Mn_(1.5)Al has the highest shear modulus and Young's modulus, with values of 98.8 GPa and 259.2 GPa, respectively. These Fe–Mn–Al alloys display disparate anisotropies due to the calculated different shape of the three-dimensional curved surface of the Young's modulus and anisotropic index. Moreover, the anisotropic sound velocities and Debye temperatures of these Fe–Mn–Al alloys were explored.     

Effects of alloying element on stabilities,electronic structures,and mechanical properties of Pd-based superalloys

The thermodynamic stabilities, electronic structures, and mechanical properties of the Pd-based superalloys are studied by first principles calculations. In this work, we discuss the effect of Pd-based superalloys made from Al, Si, Sc, Ti,V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, Mo, Tc, Hf, Ta, W, Re, Os, Ir and Pt, and we also calculate a face centered cubic(fcc)structure 2 × 2 × 2 superalloy including 31 Pd atoms and one alloying element T M(Pd_(31)TM). The mixing energies of these Pd-Based superalloys are negative, indicating that all Pd-based superalloys are thermodynamically stable. The Pd_(31)Mn has the lowest mixing energy with a value of-0.97 eV/atom. The electronic structures of the Pd-based superalloys are also studied, the densities of states, elastic constants and moduli of the mechanical properties of the Pd-based superalloys are determined by the stress-strain method and Voigt–Reuss–Hill approximation. It is found that Pd_(31)TM is mechanically stable, and Pd_(31)Tc has the largest C_(11), with a value 279.7 GPa. The Pd_(31)Cr has the highest bulk modulus with a value of299.8 GPa. The Pd_(31)Fe has the largest shear modulus and Young's modulus with the values of 73.8 GPa and 195.2 GPa,respectively. By using the anisotropic index, the anisotropic mechanical properties of the Pd_(31)T M are discussed, and threedimensional(3 D) surface contours and the planar projections on(001) and(110) planes are also investigated by the Young modulus.     

湿磨工况下冲击功对高锰钢腐蚀磨损交互作用的影响

采用自制的冲击腐蚀磨损试验机模拟湿磨工况,通过电化学等方法研究了冲击工况条件下高锰钢在锡矿浆料中的腐蚀磨损行为,定量分析了腐蚀磨损中交互作用各个分量的相对比例.结果表明,虽然弱酸性的矿浆对高锰钢的腐蚀性较小,但腐蚀增量是静态腐蚀率的15.76～26.54倍,腐蚀磨损交互作用的比例为12.08%～26.70%,表明磨损与腐蚀有一定的协同促进作用.在低冲击功1 J时,交互作用是以磨损促进腐蚀为主;在冲击功为2、3、4 J时,交互作用是以腐蚀促进磨损为主.最后探讨了冲击载荷下磨损与腐蚀的交互作用机理,以及冲击功对交互作用机理的影响.     

PIIID复合强化处理轴承钢表面TiN膜层的XPS表征

用等离子体浸没离子注入与沉积(PIIID)复合强化新技术在AISI52100轴承钢基体表面成功合成了硬而耐磨的氮化钛薄膜。膜层表面的化学组成和相结构分别用X射线衍射(XRD)和X射线光电子能谱(XPS)表征;膜层表面的原子力显微镜(AFM)形貌显示出TiN膜结晶完整,结构致密均匀。XRD测试结果表明,TiN在(200)晶面衍射峰最强,具有择优取向。Ti(2p)的XPS谱峰泰勒拟合分析揭示出,Ti(2p_1/2)峰和Ti_2p3/2峰均有双峰出现,表明氮化物中的Ti至少存在不同的化学状态;N(1s)的XPS谱峰在396.51, 397.22和399.01 eV附近出现了三个分峰,分别对应于TiNO_y,TiN和N—N键中的氮原子。结合O(1s)的XPS结果,证实膜层中除生成有稳定的TiN相外,还有少量钛的氧化物和未参与反应的单质氮。整个膜层是由TiN,TiO₂,Ti—O—N化合物和少量单质氮组成的复合体系。