钛合金表面激光熔敷Ti2Ni3Si/NiTi耐磨涂层组织与耐磨性能

以Ti-50Ni-10Si合金粉末为原料，利用激光熔敷技术在钛合金BT9基材表面制得由Ti2Ni3Si初生树枝晶和枝晶间Ti2Ni3Si／NiTi共晶组织组成的耐磨材料涂层，研究了涂层的显微组织及室温耐磨性能。结果表明，该涂层在室温干滑动磨损条件下具有优异的耐磨性能和良好的载荷特性。     

激光熔炼Ti5Si3／NiTi金属间化合物合金的组织及耐磨性

设计并利用激光熔炼技术制备出了以Ti5Si3为增强相、以NiTi为基体的金属间化合物新型耐磨合金，研究了增强相Ti5Si3的含量对合金显微组织、显微硬度及耐磨性能的影响。结果表明，随Ti5Si3含量的增加，合金显微组织由亚共晶向共晶、过共晶转化，增强相Ti5Si3由细层片状共晶相向块状初生相转变，合金显微硬度随之显著提高；在室温干滑动磨损条件下，Ti5Si3／NiTi金属间化合物合金具有优异的耐磨性，并随Ti5Si3增强相的增加而显著提高。Ti5Si3增强相的高硬度和NiTi基体的高韧性及伪弹性效应是该合金具有优异耐磨性能的主要原因。     

Microstructural evolution during containerless rapid solidification of Ni–Mo eutectic alloys

Ni–45%Mo hypoeutectic, Ni–47.7%Mo eutectic and Ni–50%Mo hypereutectic alloys are rapidly solidified during containerless processing in drop tube. The microstructures of Ni–47.7%Mo eutectic alloy are composed of lamellar eutectic plus anomalous eutectic of Ni and NiMo phases. When the droplet size decreases, the volume fraction of anomalous eutectic becomes larger. The structural morphology transforms into Ni dendrite plus lamellar eutectic in very small droplets which are highly undercooled. The microstructures of Ni–45%Mo hypoeutectic alloy are characterized by primary Ni dendrite plus lamellar eutectic, whereas those of Ni–50%Mo hypereutectic alloy consist of NiMo dendrite plus lamellar eutectic. For both off-eutectic alloys, the experimental results show that the microstructure evolution depends mainly on droplet size. In the case of Ni–45%Mo hypoeutectic alloy, with the decrease of droplet size, the primary Ni phase transforms from dendrites to equiaxed grains. As for Ni–50%Mo hypereutectic alloy, when droplets become smaller and smaller the microstructural transition proceeds from primary NiMo dendrite plus lamellar eutectic to anomalous eutectic. The calculated highest undercoolings of the three alloys are 226, 182 and 135 K, respectively. By classical nucleation theory, Ni phase is the primary phase to nucleate for Ni–47.7%Mo eutectic alloy. The TMK eutectic growth and LKT/BCT dendritic growth theories are applied to analyze the rapid solidification process and investigate the microstructural transition mechanisms. The coupled zone of Ni–Mo eutectic alloy has also been calculated on the basis of TMK and LKT/BCT models, which covers a composition range from 45.7% to 57.1% Mo.     

Ti2Ni3Si/NiTi金属间化合物合金在H2SO4溶液中的腐蚀行为

利用激光熔炼材料制备技术,制得了由三元金属硅化物Ti2Ni3Si初生枝晶和枝晶间Ti2Ni3Si/Ti共晶组成的金属间化合物耐磨耐蚀合金;采用极化曲线、塔菲尔图(Tafel Plot)和交流阻抗(EIS)等技术,研究了合金在1 mol/L H2SO4溶液中的电化学腐蚀行为以及Ti含量对合金组织与耐蚀性的影响.结果表明:由于表面形成的稳定钝化膜及Ti2Ni3Si和NiTi的高化学稳定性,使合金在1 mol/L H2SO4溶液中具有优异的耐蚀性,且随着Ti含量的升高,合金的耐蚀性略有提高.     

Variation of microstructure of RE-containing AlSi20Cu2Ni1RE0.6 alloy with different cobalt contents

Cobalt is generally considered as the element that can promote the high-temperature mechanical properties of Al-Si alloys. In order to develop new hypereutectic Al-Si alloys that can be used at high temperature, the changes of microstructure of Al-20Si-2Cu-1Ni-0.6RE-xCo alloy with different contents of Co were studied in this paper. The results show that, under P-RE complex modification of the alloy melt, the content of Co varying from 0 to 1.5% had little influence on the refining effect of primary Si and modification effect of eutectic Si, but the amount of acicular RE-bearing Al-RE-Ni-Co-Si compounds gradually increased with the increase of Co content. In addition, Co could also modify the morphology of Fe-bearing phases, which solidified as particles instead of long needles. The addition of Co even has an adverse effect on the tensile strength of this RE-containing hypereutectic Al-Si alloy.     

Effect of Zr addition on microstructures and mechanical properties of Ni-46Ti-4Al alloy

The microstructures and mechanical properties of Ni-(46-x)Ti-4Al-xZr (x = 0-8, at.%) alloys have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and mechanical tests. The results show that the Ni-Ti-Al-Zr alloys are composed of TiNi and (Ti, Al) 2 Ni with Zr as a solid solution element in both phases, and the third phase, (Zr, Ti, Al) 2 Ni, appears in Ni-40Ti-4Al-6Zr and Ni-38Ti-4Al-8Zr alloys. The compressive yield strength at room temperature increases with the increase of Zr content due to the solid-solution strengthening of Zr and precipitation strengthening of (Ti, Al, Zr) 2 Ni phase. However, the Ni-42Ti-4Al-4Zr alloy exhibits the maximum compressive yield strength at 873 and 973 K because of the softening of (Zr, Ti, Al) 2 Ni phase in the alloys with more Zr addition. The tensile stress-strain tests and the SEM fracture surface observations show that the brittle to ductile transition temperature of Ni-42Ti-4Al-4Zr alloy is between 873 and 923 K.     

激光熔化沉积Ti5Si3/NiTi双相金属间化合物合金耐磨性能

采用激光熔化沉积工艺制备出以块状Ti5Si3过渡金属硅化物为初生相、以Ti5Si3/NiTi共晶为基体的双相金属间化合物耐磨合金,在室温干滑动磨损条件下测试了Ti5Si3/NiTi合金的耐磨性能并讨论了其磨损机制。结果表明,由于Ti5Si3/NiTi合金良好的强韧性配合以及在磨损过程中磨损表面上形成了“无组织特征”的表面高硬度层,对合金有保护作用,合金在室温干滑动磨损条件下具有优异的耐磨性能和很低的载荷敏感性     

钛硅共晶系合金的微观组织与断裂特征

钛硅共晶系合金的组织形态与传统铸造钛合金组织完全不同，随着Si含量的增多合金塑性变差；断口形貌显示，合金的断裂为明显的脆性断裂，但不同类型的合金断裂机制又不尽相同。试验测试了亚共晶Ti-7%Si合金的共晶Ti-8.5%Si合金的室温和高温拉伸性能。     

NiTi合金的电子结构及缺陷作用的符合正电子湮没研究

利用双探头符合系统，测量了纯金属Si、Ni、Ti以及5种不同成分的NiTi合金的正电子湮没辐射Doppler展宽谱，计算了NiTi合金的形参数。结果表明，当Ni原子和Ti原子形成NiTi合金时，两原子中均有部分3d电子被局域化并形成共价键，导致合金基体中参与形成金属键的自由电子减少。在NiTi合金中金属键和共价键同时存在。成分为Ni-49at％Ti合金的W参数最高，表明该成分的合金中所含的缺陷数量最少，这可能是该成分合金形状记忆效应较好的原因。     

双晶体NiTi形状记忆合金在无/有应力作用时效下的Ni_4Ti_3相沉淀行为模拟(英文)

运用相场方法研究双晶体NiTi形状记忆合金分别在无应力和有应力作用下时效过程中Ni4Ti3相的沉淀行为,模拟研究两种不同初始过饱和度(Ni含量分别为51.5%和52.5%,摩尔分数)的NiTi基体并考虑外加应力的影响。模拟结果表明,在无应力作用的体系中,当体系Ni原子初始浓度相对较低(51.5%Ni)时,Ni4Ti3相以非均匀的方式析出,其中晶界上存在大量的Ni4Ti3变体,晶界内大部分区域无变体;当体系Ni原子初始浓度较高(52.5%Ni)时,Ni4Ti3在整个双晶体系中均匀析出。在所研究的两种初始浓度下,一定大小的外加应力将直接导致Ni4Ti3变体在整个模拟体系中均匀析出,而两晶粒中变体的类型分布有所不同。     

Microstructure characteristics of Ni-43Ti-4Al-2Nb-2Hf alloy prepared by conventional casting and directional solidification

To further investigate the microstructure characteristic and solidification mechanism,so as to provide knowledge for the microstructure control of a NiTi-Al based high-temperature structural material,t...     

Microstructural change in gravity cast Mg−Ni alloys with Ni contents

The effects of Ni content on the microstructures of gravity cast Mg−Ni alloys were examined. Different shapes of primary solid particles and microstructures of the eutectic matrix were observed with varying Ni content. The eutectic matrix in the hypoeutectic alloy consisted of rod-like Mg₂Ni phase with a small amount of α-Mg phase. The eutectic matrix in the near-eutectic and hypereutectic alloys consisted of eutectic cells oriented in different directions. A transition of lamellae to fiber occurred. The formation of cellular structure and transition of lamellae to fiber resulted from two-phase instability in the coupled region induced by constitutional undercooling.     

激光熔覆Mo2Ni3Si／NiSi金属硅化物复合材料涂层组织与耐磨性

以39Mo-35Ni-26Si(w％)合金粉末为原料，采用激光熔覆技术，在1Cr18Ni9Ti不锈钢基材表面翩得以Mo2Ni3Si金属硅化物为初生相，以Mo2Ni3Si／NiSi共晶相为基体的金属硅化物耐磨复合材料涂层。涂层的常温干滑动磨损试验结果表明，在磨损过程中，Mo2Ni3Si／NiSi共晶相轻微地优先磨损，Mo2Ni3Si金属硅化物微微凸出于磨损表面，起到抗磨的骨干作用。由于Mo2Ni3Si金属硅化物具有很高的硬度和很强的原子间键合力，在磨损过程中难于变形和粘着，激光熔覆Mo2Ni3Si／NiSi金属硅化物复合材料涂层具有优异的耐磨性，与1Cr18Ni9Ti标样相比，涂层的耐磨性提高了56倍。     

Microstructural evolution of direct chill cast Al-15.5Si-4Cu-1Mg-1Ni-0.5Cr alloy during solution treatment

Heat treatment has important influence on the microstructure and mechanical properties of Al-Si alloys. The most common used heat treatment method for these alloys is solution treatment followed by age-hardening. This paper investigates the microstructural evolution of a direct chill (DC) cast Al-15.5Si-4Cu-1Mg-1Ni-0.5Cr alloy after solution treated at 500, 510, 520 and 530℃, respectively for different times. The major phases observed in the as-cast alloy are α-aluminum dendrite, primary Si particle, eutectic Si, Al7Cu4Ni, Al5Cu2Mg8Si6, Al15(Cr, Fe, Ni, Cu)4Si2 and Al2Cu. The Al2Cu phase dissolves completely after being solution treated for 2 h at 500℃, while the eutectic Si, Al5Cu2Mg8Si6 and Al15(Cr, Fe, Ni, Cu)4Si2 phases are insoluble. In addition, the Al7Cu4Ni phase is substituted by the Al3CuNi phase. The α-aluminum dendrite network disappears when the solution temperature is increased to 530℃. Incipient melting of the Al2Cu-rich eutectic mixture occurrs at 520℃, and melting of the Al5Cu2Mg8Si6 and Al3CuNi phases is observed at a solution temperature of 530℃. The void formation of the structure and deterioration of the mechanical properties are found in samples solution treated at 530℃.     

激光熔敷Ti5Si3／NiTi金属间化合物复合材料涂层组织与耐磨性

以Ti14Si6Ni80合金粉末为原料，利用激光熔敷技术在BT9钛合金表面制得以金属硅化物Ti5Si3为增强相、以金属间化合物NiTi为基体的快速凝固金属间化合物复合材料涂层，分析了该涂层的显微组织，在室温干滑动磨损条件下测试了其耐磨性。研究结果表明，涂层硬度高、组织致密、与基材之间为完全冶金结合，在干滑动磨损试验条件下具有较好的耐磨性。涂层具有优异耐磨性的主要原因是作为耐磨增强相的金属硅化物Ti5Si3具有高硬高耐磨的特性，在涂层中起到了抗磨骨干作用，同时作为涂层基体的金属间化合物NiTi由于具有极强的原子结合键及应力诱发马氏体相变特性，本身具有优异的耐磨性，在摩擦过程中对耐磨增强相Ti5Si3起到了强力支撑作用。     

Fourier Thermal Analysis of the Eutectic Formed in Pb-Sn Alloys

The effect of the presence of two different primary phases on the microstructural characteristics and solidification kinetics of Pb-Sn eutectic was analyzed using Fourier thermal analysis method (FTA) and microstructural characterization. Three Pb-Sn alloys, a hypoeutectic, an eutectic, and a hypereutectic alloy, were melted in an electric furnace under an argon atmosphere and poured into sand molds. Cooling curves were obtained and numerically processed using FTA. Microstructural observations of the probes indicate a lamellar morphology for the eutectic microconstituent of the hypereutectic alloy; the eutectic alloy shows the presence of both lamellar and anomalous eutectic and the hypoeutectic alloy shows only the presence of anomalous eutectic. FTA results indicate that in the case of the probes showing the presence of anomalous eutectic, there is a primary eutectic formed during recalescence at high undercooling and a secondary eutectic yielded at low undercooling at the eutectic plateau temperature. This result shows that the cause behind the observed differences in the eutectic morphologies of the experimental alloys lies on the nucleating ability of the primary phase available as a potential substrate for nucleation of the eutectic microconstituent.     

AlCrCuFeNbxNiTi高熵合金组织与性能研究

采用电弧熔炼制备了AlCrCuFeNb_xNiTi (x = 0, 0.25, 0.5, 1.0)高熵合金,研究不同Nb含量对AlCrCuFeNb_xNiTi高熵合金显微组织和力学性能的影响。研究表明：AlCrCuFeNb_xNiTi (x = 0, 0.25, 0.5, 1.0)高熵合金物相主要包含有序FCC的L2₁相和Laves相,还有少量的BCC(A2)和FCC相;Nb元素的添加能促进Laves相的生成且对Cu元素的偏析具有一定的抑制效果;通过相判据参数计算找到了适合AlCrCuFeNb_xNiTi高熵合金的相形成判据;添加适量的Nb元素能够改善AlCrCuFeNiTi六元高熵合金的力学性能;AlCrCuFeNb_0.5NiTi 高熵合金具有较好的综合力学性能,抗压强度达到1587.4 MPa,硬度达到568.8 HV;Nb元素含量过高时会形成过多的Laves相使合金表现出过早脆化现象。     

Effects of Ti addition and heat treatments on mechanical and electrical properties of Cu-Ni-Si alloys

The mechanical and electrical properties of Cu-5.98Ni-1.43Si and Cu-5.98Ni-1.29Si-0.24Ti alloys under heat treatment at 400 and 500 °C after hot- and cold-rolling were investigated, and a microstructural analysis using transmission electron microscopy was performed. Cu-5.98Ni-1.29Si-0.24Ti alloy displayed the combined Vickers hardness/electrical conductivity value of 315.9 Hv/57.1%IACS. This was attributed to a decrease of the solution solubility of Ni and Si in the Cu matrix by the formation of smaller and denser δ-Ni₂Si precipitates. Meanwhile, the alloyed Ti was detected in the coarse Ni-Si-Ti phase particles, along with other large Ni-Si phase particles, in Cu-5.98Ni-1.29Si-0.24Ti.     

多主元高熵合金AlTiFeNiCuCrx微观结构和力学性能

研究了不同Cr含量的AlTiFeNiCuCrx多主元高熵合金的微观组织和力学性能特点.结果表明,Cr含量的增加使合金的凝固模式从亚共晶向过共晶凝固转移,铸态组织由先析出枝晶相、菊花状共晶组织和枝晶间相组成.合金仅由简单的体心立方结构和面心立方结构两相组成.Cr含量的增加对合金硬度的提高较小.该合金为低温脆性材料,但在1073 K高温时具有很好的塑性变形能力和较高的强度,当x=1-1.5时,合金具有最优的压缩强度和塑性组合.     

Microstructure and Mechanical Properties of Cr2Nb-Based Laves Phase Alloys Prepared by Laser Surface Remelting

The microstructure and mechanical properties of Cr₂Nb-based intermetallic matrix composites fabricated by laser surface remelting were investigated at hypoeutectic and hypereutectic compositions. In the hypoeutectic composition, the molten zones under different laser scanning velocities consist of fully α-Cr dendrites, whereas a series of morphology evolutions perpendicular to the scanning direction occurred in the hypereutectic composition: Cr₂Nb primary phase + Cr/Cr₂Nb eutectic → Cr/Cr₂Nb eutectic → α-Cr primary phase + Cr/Cr₂Nb eutectic → fully α-Cr dendrite. Based on the maximum growth rate criterion, the microstructure evolutions of the molten zones were analyzed by considering the competitive growth among the α-Cr phase, Cr₂Nb Laves phase, and the Cr/Cr₂Nb eutectic, which are in agreement with the experimental results. More importantly, the room-temperature fracture toughness values of the hypoeutectic and hypereutectic alloys attain 11.2 MPa m^1/2 and 7.9 MPa m^1/2, respectively, which increase by eight and six times over the as-cast Cr₂Nb Laves phase (1.2 MPa m^1/2), respectively. The remarkable enhancements in room-temperature fracture toughness were explained in terms of fine-grain toughening, second Cr phase toughening, and point defects toughening.