ZrB2-SiC-AlN陶瓷基复合材料的组织及性能

选用AIN作烧结助剂,采用热压烧结技术制备了ZrB2+20%SiC+η%AIN陶瓷基复合材料.利用SEM等手段对其组织进行了分析,并对其力学性能和高温烧蚀性能进行了分析测试.     

ZrB2-SiC-AIN陶瓷基复合材料的组织及性能

选用AIN作烧结助剂，采用热压烧结技术制备了ZrB2＋20％SiC＋η％AIN陶瓷基复合材料。利用SEM等手段对其组织进行了分析，并对其力学性能和高温烧蚀性能进行了分析测试。     

机械合金化制备纳米ZrB2-TiB2复合粉末

本文采用Zr、Ti、B为原料（摩尔比：1:1:4）,在氩气气氛保护下,采用机械合金化方式,在球料比10:1、球磨转速500 rpm实验条件下制备了纳米结构的ZrB2-TiB2。文章采用X射线衍射仪（XRD）、场发射扫描电镜（FESEM）,透射电镜（TEM）仪器,对不同球磨时间粉末的相组成、微观结构进行了表征。结果发现,原始粉末经120小时球磨后,粉末主要由ZrB2和TiB2组成,平均尺寸再20纳米左右,TiB2 分布于ZrB2基体上。文章还探讨了该体系获得目标产物的机械合金化机制。     

Microstructure and hydrogen storage properties of Mg-Sn nanocomposite by mechanical milling

To improve the hydrogen storage properties, the composition and microstructure of Mg-Sn alloys were modified through fabricating Mg/Mg₂Sn nanocomposite by mechanical alloying. The microstructures were characterized by X-ray diffraction and scanning electron microscopy. It is found that Mg₂Sn instead of Mg(Sn) solid solution is preferably formed during milling process. Although Mg₂Sn is not a hydriding phase, the in situ formed nanosized Mg₂Sn facilitates hydrogen absorption/desorption of Mg by forming Mg/Mg₂Sn nanocomposite. The mechanically milled Mg-5 at.% Sn nanocomposite exhibits slightly elevated plateau pressure and destabilized thermodynamics due to the introduction of large amount of interface energy in Mg/Mg₂Sn nanocomposite.     

(ZrAl3+ZrB2)/Al复合材料的制备和微观组织结构

采用混合盐反应法,以KBF4和K2ZrF6粉剂为原料在铝熔融体中制备了(ZrAl3 ZrB2)/Al复合材料.借助于X射线衍射仪、电子探针和透射电镜对复合材料的物像和增强相进行了观察,结果表明ZrB2颗粒呈等轴或等轴颗粒状,为六方结构,尺寸大部分小于1μm,ZrAl3相大部分呈长条状,两种增强相整体分布较为均匀,且与Al的界面光滑洁净,没有其它界面生成物.对复合材料的硬度做了测试,原位合成增强相的引入显著提高了复合材料的HRB硬度.     

原位TiB增强ZrB2-SiC接头的界面组织和力学性能

以Ag-Cu共晶箔和Ti箔的叠层箔片为中间层,实现了ZrB2-SiC复合陶瓷自身的连接。扫描电镜和能谱分析表明:液态钎料中的Ti能够与ZrB2反应,在陶瓷表面原位生成了具有定向分布的TiB晶须,接头的典型界面结构为ZS/TiB(Ag(s,s))/TiCu(AgCu4Zr)/Ag(s,s)/TiCu(AgCu4Zr)/TiB(Ag(s,s))/ZS。研究了不同温度下接头的组织演化规律,发现ZrB2在液态钎料中的分解温度为860℃,TiB晶须的生成温度为880℃。接头在900℃下保温10 min获得最高抗剪强度134 MPa。较高的强度主要得益于原位TiB晶须阵列对陶瓷表面应力的调节,以及形成陶瓷向焊缝中心的梯度过渡。     

Microstructure and mechanical properties of pulsed DC magnetron sputtered nanocomposite Cr-Cu-N thin films

The nanocomposite Cr-Cu-N thin films have been deposited at a substrate temperature of 250 °C by a bipolar asymmetric pulsed DC reactive magnetron sputtering process. Different Cu contents ranging from 0.4 to 14.9 at.% were achieved. The structures of Cr-Cu-N thin films were analyzed by XRD. The surface and cross sectional morphologies of thin films were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The nanoindentation and scratch tests were adopted to evaluate the mechanical and tribological properties of Cr-Cu-N coatings. The influences of Cu content on the structure, mechanical and tribological properties of Cr-Cu-N coatings were explored. It is observed that the columnar structure no longer exists when the Cu content exceeds 10.9 at.%. The stability of CrN phase in the coating is influenced by the Cu content. The scratching coefficient of thin films decreases with increasing Cu content. Sufficient adhesion and tribological properties of Cr-Cu-N coatings are achieved. The maximum average hardness around 20 GPa and scratching coefficient around 0.1 are found in the coatings with around 2.1 to 2.6 at.% Cu in this work.     

Microstructure and high-temperature wear behavior of laser clad Ni-Ti-Si ternary metal silicide coatings

Ni-Ti-Si ternary metal silicide coatings were fabricated on AISI 304 stainless steel by laser cladding process. The coatings consisted of Ni₁₆Ti₆Si₇ primary dendrite and interdendritic Fe-Ni-based solid solution γ and exhibited excellent abrasive and adhesive wear resistance under high temperature metallic dry sliding wear conditions. The excellent wear properties were attributed to the high hardness and covalent dominant atomic bond of the metal silicide Ni₁₆Ti₆Si₇. The dominant wear mechanism of the coating were delamination of the coating and material transfer from the mating surface.     

Kinetics of phase separation in iron-based ternary alloys. I. Theoretical analysis of phase separation behavior in iron-based ternary alloys

Phase sepation behavior in an Fe-based ternary system was investigated by using a model based on the Cahn–Hilliard equation. The asymptotic behavior of the minor element, Y, in an Fe–X–Y ternary alloy along a trajectory of a peak top of the major element, X, is classified into three groups according to the sign of the second derivative of the chemical free energy f₁ with respect to the concentration of X, c_X and the concentration of Y, c_Y, f′_XY≡∂²f₁/∂_CX∂_CY. If f′_XY>0,, the value of c_Y along the trajectory of the peak top of Y decreases with time. When f′_XY<0 at 0t<∞, peaks of c_Y formed at the peak tops of Y. The amplitute of the peak increases with time. In the case that f′_XY<0 at 0t<t₀and f′_XY>0 at t₀<t<∞, peaks of c_Y formed at the peak tops of Y at the initial stage. Bifurcation of peaks occurs. The concentration of the major element, c_X, along the trajectory of its peak increases with time regardless of the sign of f′_XY.     

粉末冶金碳化物强化铌合金组织演变及其力学行为

采用机械球磨与热压烧结相结合的粉末冶金法对不同球磨时间Nb-35Ti-6Al-5Cr-8V-5C合金的粉末变形行为,微观组织结构和力学行为进行研究。结果表明:随着球磨时间的增加,Nb-35Ti-6Al-5Cr-8V-5C复合粉末中的块状金属颗粒首先变形为片状后在碰撞挤压作用下破碎成絮状,TiC粉末均匀的分布于片状金属粉末表面;Nb-35Ti-6Al-5Cr-8V-5C合金由Nbss和(Nb,Ti)C两相构成,各合金碳化物体积分数均为11%左右,Ti元素主要分布于Nbss晶界和碳化物内,Al、Cr、V元素主要分布于Nbss晶粒内,Nbss和(Nb,Ti)C相尺寸均随球磨时间增加而尺寸减小;Nbss晶粒细化及强化相碳化物弥散化导致合金的室温压缩力学性能和塑性变形能力显著提高,压缩变形后合金Nbss与碳化物具有良好的界面结合能力,但是碳化物内部存在明显的近似平行分布的裂纹;数据对比表明,粉末冶金法制备Nb-35Ti-6Al-5Cr-8V-5C合金的力学性能优于电弧熔炼法。     

激光熔覆ZrB2-SiC增强Cu基复合涂层的微观结构与摩擦学性能

为了提高铜表面的强度和耐磨性,以复合粉末(Zr、Si、Ni包B4C、Cu)为原料,采用激光辅助原位合成技术,在纯铜基体表面制备了ZrB₂-SiC/Cu复合涂层。通过XRD、SEM和TEM分析了复合涂层的表面形貌、微观结构、相组成和界面结合,并测试了不同增强相含量熔覆层的硬度和摩擦学性能。结果表明：通过设计的原位化学反应成功在铜基体内合成了微米级针状ZrB₂和纳米级颗粒状SiC。增强相均与基体形成了清洁、无杂相的界面。2种不同维度与尺寸的增强体,通过多种强化机制,显著改善了复合涂层的力学性能;通过调整激光工艺参数可实现增强体尺寸的控制,随着增强相含量的提高,复合涂层的平均硬度和耐磨损性逐渐增加。当增强相含量为30%(质量分数,下同)时,复合涂层的平均硬度(HV0.2)为3028 MPa,约为纯铜的5.6倍。30%增强相涂层的载流磨损率与10%增强相的涂层相比,降低了约80%。较高含量增强相的复合涂层表现出优异的摩擦学性能。     

Oxidation behavior of ZrB2 composites doped with various transition metal silicides

This paper deals with the oxidation behavior of ZrB₂-based composites sintered with different additives, namely ZrSi₂, MoSi₂, TaSi₂ and WSi₂. The oxidation mechanisms were investigated between 1200 and 1800 °C for 15 min in a bottom loading furnace. The scope of this study is to draw a classification of goodness for the 4 composites depending on the temperature range and understand how each cation influences the oxidation behavior of ZrB₂ by acting either on glass or on ZrO₂ modification. MoSi₂ was the best additive for improving the oxidation resistance of ZrB₂, even up to 1800 °C.     

Relationship between dispersibility of ZrO2 nanoparticles in Ni-ZrO2 electroplated nanocomposite coatings and mechanical properties of nanocomposite coatings

Ni-ZrO2 nanocomposite coatings with monodispersed ZrO2 nanoparticles were prepared from the composite plating bath containing dispersant under DC electrodeposition condition. It is found that the morphology, orientation and hardness of the composite coating with monodispersed ZrO2 nanoparticles have lots of difference from the composite coating with agglomerated ZrO2 nanoparticles and pure nickel coating. Especially, the result of hardness shows that only a very low volume fraction (less than 1%) of monodispered ZrO2 nanoparticles in Ni-ZrO2 composite coatings will result in higher hardness of the coating. The hardness of Ni-ZrO2 nanocomposite coatings with monodispersed and agglomerated ZrO2 nanoparticles are HV 529 and HV 393, respectively. The hardness value of the former composite coatings is over 1.3 times higher than that of the later. All these composite coatings are 2 - 3 times higher than that of pure nickel plating (HV 207) prepared under the same conditions.     

Microstructure and mechanical behavior of NiAl-based alloy prepared by powder metallurgical route

Rapidly solidified NiAl–28Cr–6Mo–B–Dy prealloyed powder doped with Nb powder was consolidated by hot pressing under 1250 °C for 30 min at 30 MPa. The consolidated material exhibited a different microstructure from the original powder, i.e. the NiAl and Cr(Mo) plates in the eutectic cell tend to break down into short platelets or even particles during hot pressing process. The mechanical behaviors at room temperature and at high temperature of consolidated sample from powder alloy were evaluated by three-point bending technique, tensile test and compressive test. The results showed that the hot pressing alloy possessed a reasonable combination of room temperature ductility and toughness, and elevated temperature strength.     

Microstructure and mechanical properties of Mg-Zn-Gd-based alloys strengthened with quasicrystal and Laves phase

One kind of Mg3.5Zn0.6Gd-based alloy strengthened with quasicrystals was designed, and the effect of alloying elements on microstructure and mechanical properties of as-cast Mg-Zn-Gd alloy at room temperature and elevated temperatures were studied. The results indicate that MgZnCu Laves phase, which coexists with quasicrystal at grain boundary, emerges with the addition of copper element in Mg-Zn-Gd alloy. The strength of alloys exhibits the parabola curve with the increase of copper content. The alloy with 1.5% （mole fraction） Cu shows better mechanical properties at room temperature： tensile strength 176 MPa, yield strength 176 MPa and elongation 6.5%. The existence of MgZnCu Laves phase can effectively improve the heat resistance and elevated temperature properties of the alloy. The alloy with 1.5% Cu has better mechanical properties at 200℃ ： tensile strength 130 MPa and elongation 18.5%. The creep test of the alloys at 200℃ and 50 MPa for 102 h indicates that Mg3.5Zn0.6Gd alloy reinforced with quasicrystal has better creep properties than AE42, which can be further improved with the introduction of Laves phase in the alloy.     

Al-Si合金瞬间液相扩散连接接头组织与力学性能

采用扫描电镜、X射线衍射、能谱仪及电子拉伸试验机等测试方法研究了Cu箔作中间层瞬间液相扩散连接(TLP)Al-Si合金接头的组织和力学性能.结果表明,Al-Si合金基体中的Al元素与中间层Cu元素发生共晶反应形成液相,而合金中的Si对Al与Cu的相互作用有一定的阻碍.接头组织主要由α-Al、单晶Si及金属间化合物(CuAl2和Al4Cu9)组成,而金属间化合物的数量随连接时间的增加而减少.剪切试样沿着界面/基体处断裂.当温度为560℃时,随着连接时间的增加,接头抗剪强度先增大后减小,在120 min时达到最大值70.2 MPa;接头塑性和韧性提高,断口表面形貌由脆性特征转变为脆性和韧性共存的混合型断裂特征.     

激光熔覆Fe-Cr-Co-W合金系熔覆层硬质相的微观形貌与摩擦行为

为分析Fe-Cr-Co-W合金系熔覆层的冶金结晶过程和耐磨硬质相的微观形貌与形成机理,解释Fe-Cr-Co-W合金系熔覆层提高耐磨性机理,采用激光熔覆工艺在Q235钢表面熔覆不同成分的Fe-Cr-Co-W系合金粉末,并获得一定厚度的熔覆层,进行了激光熔覆层金相组织分析和物相测试,对不同成分Fe-Cr-Co-W系熔覆层进行了干摩擦对比试验,研究了熔覆层的组织结构和干摩擦之后的组织形貌,并测试了硬质相的硬度。结果表明,熔覆层组织致密,与基体组织达到完全冶金结合,熔覆层结构主要为在γ-Fe基体上分布着叶脉状硬质相,结合扫描电镜能谱分析和X射线衍射分析结果,该叶脉状硬质相为Co3W3C。在M-200试验机上干摩擦后的熔覆层表面形貌中,叶脉状硬质相Co3W3C在熔覆层表面起到支撑作用,浮凸于基体组织表面,减少了基体组织的磨损,起到减磨的作用。随着W和Co元素含量的增加,叶脉状硬质相Co3W3C的含量增加,摩擦系数呈现减小的趋势,在相同的试验条件下,不同含量Fe-Cr-Co-W系熔覆层磨损最小失重是Fe-Cr系熔覆层的1/60。创新点： 增加W和Co元素可显著提高熔覆层耐磨性,最高可达60倍;分析解释了熔覆层的组织结构和形成机理,发现并着重分析了熔覆层硬质相叶脉状Co3W3C的物相组成和耐磨机理,为激光技术在金属材料零部件的失效修复和表面强化提供了理论和实践参考。     

Microstructure, phase transformation and mechanical properties of Ni-Mn-Ga-Y magnetic shape memory alloys

Influence of rare earth Y addition on the microstructure and phase transitions and mechanical properties of polycrystalline Ni₅₀Mn₂₉Ga₂₁ ferromagnetic-shape memory alloy (FSMA) are investigated. It is shown that microstructure of the Ni-Mn-Ga-Y alloys consists of the matrix and the Y-rich phase. The Y-rich phase firstly disperses homogeneously in the matrix with small amounts and then tends to segregate at the grain boundaries with increasing Y substitution for Ga. The Y-rich phase is indexed to Y(Ni,Mn)₄Ga phase with a hexagonal CaCu₅ type structure. The structural transition from 5 M to 7 M, and then to non-modulated T martensite appears with the increase of Y content. The martensitic transformation temperature increases remarkably with increasing Y content, whereas the Curie temperature almost keeps unchanged. It is revealed that the appropriate addition of Y significantly enhances the yield strength and improves the ductility of the alloys. The mechanism on the influence of Y content on the improved mechanical properties and martensitic transformation temperature is also discussed.     

Microstructure,mechanical properties and fracture behavior of Nb with minor Si addition

Controlling the content of elements in niobium solid solution (Nb_SS) is significant for better comprehensive properties of Nb-Si based alloys. In this paper, the influences of minor Si (0, 0.5, 1, 2 and 3.5 at.%) on microstructures and mechanical properties of arc melted Nb at room temperature have been investigated. The increasing addition of Si would promote grain refinement and increase Si concentration in Nb_SS. Nb₃Si and (Nb_SS + Nb₃Si) eutectic phases are found when Si content is higher than 1 at.%. With the increase of Si concentration in Nb_SS, the Vickers hardness, ultimate tensile strength (UTS) of Nb_SS increases while elongation decreases. However, the fracture toughness and UTS decrease from 1 at.% to 3.5 at.% because of the grain boundary precipitation of silicides. In addition, with Si addition from 0.5 at.% to 1 at.%, the fracture feature transforms from dimple to cleavage and reduces the elongation rapidly (23.4% to ~ 0%) because of the embrittlement of Nb_SS. Controlling Si concentration to 0.5 at.% is beneficial for strengthening the Nb_SS and retaining its good ductility and fracture toughness.     

Microstructure,mechanical properties and fracture behavior of a new WE43 alloy

The microstructures,mechanical properties and fracture behaviors of a new WE43 alloy (Mg-4Y-1.6Nd-2Sm-0.5Zr) were investigated.The microstructure of the as-cast...