扫描速度对激光快速成型316L不锈钢组织性能的影响

研究了在激光功率900W条件下，扫描速度对激光快速成型不锈钢零件组织，性能的影响，在各扫描速度下，所成型的不锈钢薄壁板件的组织均为枝晶组织，随扫描速度提高，不锈钢薄壁板的定向生长树枝晶组织细化，枝晶间距变小，同时其沿X方向的机械性能（抗拉强度及硬度）降低。     

大塑性变形对粉末冶金法制备Ag/SnO2材料性能的影响

用粉末冶金法制备Ag/SnO2材料,考察了Ag/SnO2材料在大塑性变形过程中的组织均匀化及性能变化情况.经SEM分析表明,Ag/SnO2复合材料经过大塑性变形后,聚集区的SnO2颗粒逐渐分散并均匀分布.经过性能测试和XRD分析,Ag/SnO2复合材料经过大塑性变形后,材料的抗拉强度升高,塑性改善,亚晶粒尺寸减小,使材料更容易加工;电导率随真应变呈先上升后下降的趋势.     

原位自生TiB2p/Al-18%Si复合材料的组织和性能

采用TiO2和KBF4粉体为反应物,适量Na3AlF6为覆盖剂,用熔体直接反应法制备了TiB2p/Al-18%Si复合材料,通过OM、SEM和EPMA对复合材料的相及微观组织进行研究,并测试了常温条件下复合材料的硬度、抗拉强度和干滑动摩擦磨损性能。结果表明,原位反应生成的TiB2颗粒尺寸小于1μm,且大多数在Al-18%Si合金基体中均匀分布,粗大的α-Al枝晶和针状共晶Si组织得到细化;复合材料的硬度、抗拉强度、摩擦磨损性能高于无TiB2颗粒的Al-18%Si合金。     

六方氮化硼(hBN)表面镀镍对Ni-Cr/hBN固体自润滑材料性能的影响

为了改善六方氮化硼(hBN)固体润滑剂和Ni-Cr合金基体之间的润湿性,采用硝酸镍分解-氢还原法制备Ni包覆hBN粉末(即Ni/hBN粉末).分别用Ni/hBN粉末和未包覆的hBN粉末作为固体润滑剂制备(Ni-Cr)/hBN自润滑复合材料,研究hBN粉末表面包覆Ni对该复合材料组织和性能的影响.结果表明:与hBN相比,...     

Effects of Dendrite Size on Tensile Deformation Behavior in Zr-Based Amorphous Matrix Composites Containing Ductile Dendrites

Four Zr-based amorphous matrix composites whose dendrite size was varied with plate thickness were investigated, and the deformation mechanisms related with improvement of strength and ductility were investigated by focusing on how the size of ductile ?? dendrites affected the initiation and propagation of deformation bands. These composites contained 47 to 49?vol pct of dendrites sized by 14.7 to 42.8???m, and they showed excellent tensile properties of yield strength of 1.3 to 1.5?GPa and uniform elongation up to 11.7?pct. According to the observation of tensile deformation behavior of the composite with a plate thickness of 5?mm, many deformation bands were formed inside dendrites in several directions, and the deformation bands met crossly each other to form widely deformed areas. Because the wide and homogeneous deformation in this composite beneficially worked for the tensile strength and ductility simultaneously, the optimum size of dendrites and thickness of plates were approximately 19???m and 5?mm, respectively. Considering that Zr-based amorphous matrix composites are mostly used in a plate form in their conventional applications, the current research can provide the optimum plate thickness data for their fabrication processes such as rolling, extrusion, and strip casting.     

Correlation of abrasive wear with microstructure and mechanical properties of pressure die-cast aluminum hard-particle composite

Aluminum hard particle composites were synthesized by the solidification processing technique and the composite melt was solidified using gravity and pressure die castings. An aluminum-silicon alloy (A 332.1) has been used as the matrix and silicon carbide particles (quantity: 10 wt pct, and size: 50 to 80 μm) have been used as reinforcement for synthesis of the composite. The microstructure of the pressure die cast composite is found to be finer than those of the gravity cast ones. Additionally, the distribution of SiC particles in the Al alloy matrix is found to be more uniform in the pressure die-cast composites compared to the gravity die-cast ones. The mechanical properties such as ultimate tensile strength, hardness, and ductility are observed to be superior in the case of pressure die-cast composites compared to the gravity-cast one. The two-body abrasive wear resistance of the Al-composite is also noted to be greater in the pressure die-cast composite than in the gravity-cast one. The effects of injection pressure on the mechanical properties and wear resistance of the pressure die-cast composites are examined. It is observed that the wear resistance (inverse of wear rate), hardness, and strength of the Al-SiC composites increase with the increase in injection pressure during pressure die casting. This may be due to the finer microstructure, the absence of casting defects, and the stronger interfacial bonding between the matrix and hard dispersoid in pressure die-cast composites. The wear rate of the alloys and composites is studied as a function of their hardness, strength, and Young’s modulus. It is noted that the wear rate is primarily controlled by hardness even though other mechanical properties influence the wear behavior of the materials to some extent. An attempt is made to establish an empirical relation to correlate the wear rate of material with the mechanical properties such as hardness, ultimate tensile strength, and elongation.     

热等静压法制备NbC颗粒增强45CrMoV复合材料的组织与性能

采用机械球磨和热等静压(hot isostatic press,HIP)相结合的方法制备NbC颗粒增强45CrMoV弹簧钢基复合材料(NbCp/45CrMoV),观察该材料的显微组织、增强颗粒分布和界面结合情况,检测其相对密度、硬度、拉伸性能和摩擦磨损性能,并探讨其断裂行为和磨损机理。结果表明,NbCp/45CrMoV复合材料的组织均匀细小,NbC颗粒均匀地弥散分布在基体之中,且与基体界面结合良好,相对密度达到99%以上。与45CrMoV弹簧钢相比,该材料的硬度和弹性模量增大,分别为44 HRC和208 GPa,抗拉强度略有降低,为1 250 MPa;伸长率由11%减小到2%;耐磨性能大幅提高,特别是在高载荷下,例如700 N时,质量磨损只有HIP 45CrMoV的1/4,摩擦因数有所增大。     

热等静压TiC_p/30CrNi4Mo钢基复合材料的组织与性能

采用球磨与热等静压相结合的方法制备TiC_p/30Cr Ni4Mo钢基复合材料,研究材料的显微组织、密度、硬度、常温和高温拉伸性能以及摩擦磨损性能。结果表明,TiC_p/30Cr Ni4Mo钢基复合材料的组织均匀细小,基体组织主要为细片状珠光体、铁素体和少量残余奥氏体,Ti C颗粒弥散分布在基体上,与基体结合牢固;复合材料的相对密度高达99.7%,硬度为49 HRC,抗拉强度高达1 266 MPa,伸长率为4.0%;复合材料具有较好的高温力学性能,400℃时复合材料抗拉强度仍高达1 135 MPa;在200 N载荷条件下,复合材料的耐磨损性能较原30Cr Ni4Mo材料提高约4倍,磨损形式主要表现为轻微的磨粒磨损;复合材料经950℃水淬和520℃回火后,抗拉强度高达1 325 MPa,伸长率为4.6%。     

Microstructure and Properties of Cu-Fe-Cr-Ag Alloy Prepared by Directional Solidification and Upward Continuous Casting

A Cu-Fe-Cr-Ag alloy was prepared by directional solidification (DS) and upward continuous casting (UCC) to study the effect of different casting methods on the structure and properties of Cu-Fe-Cr-Ag. The results showed that the directionally solidified Cu-Fe-Cr-Ag alloy had excellent mechanical properties and conductivity. After cold drawing and isothermal aging, the peak tensile strength (789 MPa) and peak conductivity (65.5 pct IACS) of directionally solidified Cu-Fe-Cr-Ag alloy were 21 MPa and 4.7 pct IACS higher, respectively, than those that of the upward continuously casted Cu-Fe-Cr-Ag alloy. Compared to upward continuously casted Cu-Fe-Cr-Ag alloy, the Fe dendrites in directionally solidified Cu-Fe-Cr-Ag alloy were much finer, more uniform, and arranged along the direction of the magnetic field. Cu and Ag formed a Cu-Ag eutectic structure at the edge of the directionally solidified Cu-Fe-Cr-Ag alloy rod. After multi-stage thermomechanical treatment, Ag was mainly distributed around the material and formed a structure similar to Ag-clad Cu. The directionally solidified Cu-Fe-Cr-Ag alloy had a smaller lattice constant and finer Fe fibers. The small lattice constant and Fe fibers and the special distribution of Ag lead to the excellent comprehensive performance of the directionally solidified Cu-Fe-Cr-Ag alloy.

     

Correlation of Microstructure with Mechanical Properties of Zr-Based Amorphous Matrix Composite Reinforced with Tungsten Continuous Fibers and Ductile Dendrites

A Zr-based amorphous matrix composite reinforced with tungsten continuous fibers in an amorphous LM2 alloy matrix containing ductile ?? dendrites was fabricated without pores or defects by the liquid pressing process, and its tensile and compressive properties were examined in relation with microstructures and deformation mechanisms. Overall, 68?vol pct of tungsten fibers were distributed in the matrix, in which 35?vol pct of ?? dendrites were present. The LM2 composite had the greatly improved tensile strength and elastic modulus over the LM2 alloy, and it showed a stable crack propagation behavior as cracks stopped propagating at the longitudinal cracks of tungsten fibers or ductile ?? dendrites. According to the compressive test results, fracture did not take place at one time after the yield point, but it proceeded as the applied loads were sustained by fibers, thereby leading to the maximum strength of 2432?MPa and plastic strain of 16.4?pct. The LM2 composite had the higher strength, elastic modulus, and ductility under both tensile and compressive loading conditions than the tungsten-fiber-reinforced composite whose matrix did not contain ?? dendrites. These distinctively excellent properties indicated a synergy effect arising from the mixing of amorphous matrix and tungsten fibers, as well as from the excellent bonding of interfaces between them.     

Effect of ARB Cycle Number and Second Phase Content on Mechanical properties and Microstructure of Pb–Ag Composite

A solid state method has been found for manufacturing of lead–silver composites for use as anodes in electrowinning production. Mechanical properties and microstructure of composite were characterized via peeling, tensile and microhardness tests, and scanning electron microscopy, transmission electron microscopy and fractography. Based on the peeling test results, maximum bond strength was achieved in the presence of 0.125 wt% of Ag (1.8 N/mm). Best mechanical properties were achieved in the Pb–0.5 wt% Ag composite after 10 ARB cycles by the enhanced tensile strength rising up to 50%, yield strength up to 170%, shear strength up to 63% and hardness up to 2.6 times higher, and the strain decreasing to 68% lower. These advanced properties led to higher stiffness and considerable enhancements in dimensional stability of the anodes and they improved creep characteristics. The advanced properties of the processed Pb–Ag composite anodes could be introduced as certification for slower anode failure, upkeep, surcharge and capital expenditure of industries with essential lead anode requirement.     

Effect of Zn Content on Microstructure and Mechanical Properties of MgZnYLaMM Alloys

The effect of Zn content on microstructure, existing phases, and mechanical properties of rapidly solidified MgZn _x Y₁LaMM₁Mn_0.5 alloys (X?=?2, 3, 4 at.?pct) has been investigated. To assess the microstructural characterization of nanocrystalline alloys, the study also includes microstructural characterization of the master alloys. The microstructure of the alloys in as-rapidly solidified condition consisted of supersaturated magnesium dendrites and fine (Mg,Zn)₁₇La₂ and W phase (Mg₃Y₂Zn₃) segregated at grain and cell boundaries. During continuous heating, the metastable solid solution in Mg dendrites breaks down, increasing the volume fraction of second-phase particles. After annealing for 1?hour at 673?K (400?°C), very small spherical Mn-rich precipitates appeared in the three alloys and a long-period stacking ordered (LPS) phase of rectangular morphology precipitated inside the Mg grains in the alloy with the lowest Zn content. The nanocrystalline nature of the ribbons accounts for the high hardness and yield stress values in as-rapidly solidified state, although both decrease with increasing zinc content. This fact has been related to a coarser microstructure and higher volume fraction of the W phase as the Zn content increases. The highest yield stress value of 350?MPa is attained by the MgZn₂Y₁LaMM₁ ribbon in as-rapidly solidified condition. A decrease in yield stress values (about 50?MPa) is observed for all ribbons when they are heated at 673?K (400?°C) for 1?hour.     

Microstructure and mechanical properties of RS NiCrAl melt-spun alloys

The microstructure and mechanical properties of three melt-spun NiCrAl alloy ribbons have been studied in the as-cast condition as well as after thermal treatments. The microstructure of the alloys is dendritic-microcellular in as-cast condition and phases present for 10 at.% Al and 30 at.% Al alloys are as is predicted by the equilibrium phase diagram. In the 20 at.% Al alloy, γ' has frozen in metastable form and partial ordering takes place during cooling in the solid state. After thermal treatments the ribbons generally maintain a refined microstructure; α phase precipitates are always found in β and γ' phases in 20 and 30 at.% Al alloys. The hardness of the alloys increases with aluminum content. The tensile strength at room temperature is related to the phases present in the material for each state of treatment. The alloys are brittle, a higher ductility always being obtained in the as-cast condition.     

原位反应制备Ag/TiB2复合材料

在Ti和B粉末原位反应生成TiB2条件热力学分析的基础上,采用机械合金化和粉末冶金原位合成工艺制备Ag/TiB2复合材料.采用Ag粉,Ti粉和B粉作为材料,按照Ti和B摩尔比1∶2占复合材料质量分数分别为0.5％,1.0％,3.0％和5.0％ TiB2进行配料,混合后在自制高能球磨机上球磨60h,转速为150 r·min-1,球料比为60∶1.球磨后的粉末在压力机上用模具冷压成型φ21 mm ×5 mm的块状试样,压力600 MPa,保压30 s.最后将混合粉末的压制体在900℃保温4h热压炉中进行原位反应,并通入Ar气作为保护气氛,制备了不同TiB2含量的新型Ag/TiB2复合材料,系统研究了TiB2含量对AgTiB2触头复合材料组织和性能的影响.通过X-ray衍射仪,扫描电子显微镜(SEM)和能谱仪(EDS)表征分析了Ag/TiB2复合材料的相组成及显微组织,并采用维式硬度计和涡流电导仪对硬度和导电率进行了测试.研究结果表明,采用机械合金化球磨和原位反应粉末冶金技术制备Ag/TiB2复合材料是可行的.随着TiB2含量的增加,Ag/TiB2复合材料出现明显的TiB2团聚现象,且Ag/TiB2复合材料的硬度呈现先增大后减小的趋势,在硬度值为3％时,达到最大硬度值87.1 HV,但Ag/TiB2复合材料电导率随着TiB2含量的增加逐渐下降.     

MWCNTs特征对MWCNTs/Al复合材料组织及性能的影响

采用粉末冶金法制备多壁碳纳米管(MWCNTs)增强铝(Al)基复合材料(MWCNTs/Al),研究MWCNTs的特征对MWCNTs/Al复合材料显微组织结构及性能的影响。采用X线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和拉伸实验对复合材料进行性能测试。结果表明:经过球磨混合的复合粉末中没有碳化铝(Al_4C_3)相,通过烧结和热挤压后出现Al_4C_3相。与长碳纳米管(L-MWCNTs)和短碳纳米管(S-MWCNTs)相比,镀镍碳纳米管(Ni-MWCNTs)在复合材料中分散更均匀,与Al基体的结合性更好,所得到的复合材料硬度和抗拉强度较高,抗拉强度可达到247 MPa,是纯Al的4倍。     

机械合金化制备SiC弥散强化铜基复合材料

用机械合金化(MA)制备了一种以SiC为增强相的Cu／sic复合材料,研究了机械合金化过程中SIC颗粒形貌、尺寸的变化,以及增强相的含量对复合材料抗拉强度、硬度、相对电导率及显微结构的影响。结果表明,Sic对于铜是一种有效的增强相,当SiC的质量百分含量为1％时,强化效果较佳,抗拉强度可达391MPa,相对电导率为50．2％,性能较优。     

Microstructural characteristics of the directionally-solidified Al-Al3Ni eutectic and their influence on creep fracture

The microstructure and fracture mechanisms of the directionally solidified Al-Al₃Ni eutectic were studied in depth in this investigation. Solidification experiments conducted at 3.5 cm per hr resulted in the formation of a dual-orientation microstructure in which portions of the whiskers were misaligned from the normal growth direction. This structure was found to be extremely detrimental to creep behavior. The modes by which premature specimen failure occurred were identified and the detailed fracture mechanisms were determined. Microstructures of ingots solidified nominally at rates from 3.5 to 35 cm per hr were characterized. The conditions leading to the formation of the dual-orientation microstructure were established and the microstructural variations with solidification rate and with distance along the directionally solidified ingots were observed. It was found that, even with a simple shape, care must be taken in order to produce uniform controlled microstructures and the accompanying desirable properties.     

冷变形工艺对SUS301L不锈钢组织性能的影响

对亚稳定奥氏体不锈钢SUS301L进行了不同变形量的冷轧,并分别用X射线衍射仪和MP30铁素体测量仪测出了应变诱导马氏体及其含量.采用金相显微镜观察了试样的组织演变.研究结果表明:形变马氏体在剪切带的交叉点形核,新晶核的不断形成促使了形变马氏体的长大；形变马氏体随着冷轧压下量的增加而增加；另外,抗拉强度和硬度的增加幅度相当；平均抗拉强度与平均显微硬度的比值在2.82～3.17之间.     

Microstructure and mechanical properties of rapidly solidified Fe-25%Cr-5%Al ribbons produced by planar flow casting

Catalyst substrate foils of the highly oxidation resistant Fe-25Cr-5Al alloy (mass contents in %) with a thickness ranging from 40 to 180 μm have been produced by planar flow casting. The rapidly solidified ribbons showed a monophase ferritic microstructure of columnar grains. The grain size determined over a section parallel to the ribbon wheel side ranged from 5 μm for the thin ribbons (40 μm) to 18 μm for the thicker ones {180 μm). This anisotropic columnar solidification microstructure exhibits a strong <100> fiber texture, with the fiber axis nearly perpendicular to the plane of the ribbon. The position of the maximum in the pole figure was tilted from the center point toward the casting direction. Results of uniaxial tensile tests showed that only the yield stress data of the ribbons in the as-cast condition are reproducible, whereas the ultimate tensile strength and the elongation to failure data show a wide scatter band. The fracture mode exhibits ductile features such as glide bands and dimples.     

粉末冶金法制备WC-Ni3Al复合材料的组织与性能

在WC粉末中直接添加Ni、Al元素粉末,通过在液相烧结过程中反应合成Ni3Al来制备WC-Ni3Al复合材料,对该材料进行组织结构观察及力学性能测定,分析铝含量对合金致密化和镍铝相形成种类的影响,并对材料的抗氧化性能进行测试。结果表明,制备的WC-Ni3Al复合材料具有圆钝的WC晶粒形貌,粘结相中除Ni3Al相外还有少量的NiAl和Ni相;铝含量对WC-Ni3Al材料致密度的影响主要与高熔点的NiAl的形成量有关。与普通WC-15Ni硬质合金的抗弯强度(1 900 MPa)和硬度(82.6 HRA)相比,WC-15Ni3Al复合材料具有低的室温抗弯强度和高的硬度,分别为1 170 MPa和86.5 HRA。随Ni3Al含量(质量分数)从15%增加到30%,WC-30Ni3Al复合材料的室温抗弯强度增加,而硬度降低,分别为1 660 MPa和81.7 HRA,其高温抗氧化性能比WC-30(Co-Ni-Cr)硬质合金提高1个数量级。