急冷Cu-Sn合金的快速凝固焊接接头组织特征

应用微型电容储能焊机对厚度约40~60μm的急冷Cu-x%Sn(x=7,13.5,20)合金箔进行了快速凝固焊接.观察了接头的组织形貌,理论计算了微型熔核的冷却速率,分析了熔核中气孔的成因.结果表明,储能焊能够实现急冷Cu-Sn合金箔的快速凝固焊接,形成的焊接接头组织细小致密,具有典型的快速凝固特征.熔核的存在时间仅15.5μs,其平均冷速高达107K/s,接头组织与急冷箔材一致性好.气孔是急冷Cu-Sn合金快速凝固焊接过程中产生的主要缺陷,随着合金中Sn元素含量的增加,熔核中气孔的析出倾向增大.     

粉末冶金制备Fe_(28)Ni_(28)Mn_(28)Cr_8Cu_8与Fe_(28)Ni_(28)Mn_(28)Cr_8Al_8高熵合金的微观组织与力学性能

采用"机械合金化(MA)+放电等离子烧结(SPS)"的方法制备出Fe_(28)Ni_(28)Mn_(28)Cr_8Cu_8和Fe_(28)Ni_(28)Mn_(28)Cr_8Al_8两种高熵合金块体,并研究其微观组织和力学性能。结果表明:两种高熵合金均在机械合金化后形成了FCC+BCC相的合金粉末。与Fe_(28)Ni_(28)Mn_(28)Cr_8Cu_8合金相比较,当Cu元素被Al元素取代之后,Fe_(28)Ni_(28)Mn_(28)Cr_8Al_8高熵合金粉末中BCC结构的固溶体相含量明显增加。经SPS烧结后,Fe_(28)Ni_(28)Mn_(28)Cr_8Cu_8由单相FCC和少量富Cr相组成;Fe_(28)Ni_(28)Mn_(28)Cr_8Al_8则形成双相FCC结构。同时,两种高熵合金在室温下均表现出良好的压缩性能;相较于Fe_(28)Ni_(28)Mn_(28)Cr_8Cu_8,Fe_(28)Ni_(28)Mn_(28)Cr_8Al_8的屈服强度由716 MPa提高到1181 MPa,抗压强度由1908 MPa提高为2111 MPa,硬度也由267 HV上升到482 HV,但塑性却由38.6%降至26.1%。     

Ta1/Ta8Ni30Cr20Cu42/0Cr18Ni9储能焊接头组织与性能

针对钽与钢之间因物化性能差异大，储能焊接头易产生脆性金属间化合物等问题，依据熔核金属高熵化技术思路，以等摩尔比的Ta₂₀Fe₂₀Ni₂₀Cr₂₀Cu₂₀合金为熔核目标成分，依据焊接过程两种母材熔合比折合得到Ta₈Ni₃₀Cr₂₀Cu₄₂中间层合金，将其用于Ta1/0Cr18Ni9的储能焊连接. 结果表明，熔核金属的高熵合金化可有效地抑制熔核中脆性金属间化合物的形成，Ta1/Ta₈Ni₃₀Cr₂₀Cu₄₂/0Cr18Ni9储能焊接头形貌完整，熔核呈规则的杯形，长径约0.6 mm，整体向钢侧发生了偏移. 熔核组织以简单FCC固溶体为主相，兼有少量BCC固溶体. 熔核中心凝固组织以细小的等轴晶为特征，熔核与两侧母材熔合区则形成了平行生长的柱状晶，熔核区与母材结合良好. 在焊接电压1 000 V，电容500 μF，电极力30 N工艺条件下，接头平均抗剪强度372 MPa.     

Morphological Characteristic and Formation Mechanism of Joint of Meltspun Cu—Sn Alloy Foils By Capacitor Discharge Welding

应用自制的微型电容储能电阻焊帆研究了快速凝固Cu-20％Sn包晶合金的储能焊连接行为及接头组织特征．微型接头由熔核区、半熔化区及热影响区组成，熔核为以细密β‘～Cu5．6Sn等轴晶为主相的快速凝固组织，熔合区宽度仅2．0—3．0μm，热影响区组织未发生明显变化，储能焊接头组织与快速凝固箔材一致性好．在电极压力及电磁力的共同作用下，过冷熔核中发生了一定程度的液相流动，形成以加压电极为对称轴向四周辐射，并以结合面为对称面，向侧面延伸的弯曲流线．气孔是快速凝固Cu—Sn合金储能焊接头主要的焊接缺陷．随电极压力的增大，气泡半径急剧减小，当电极压力大于1．0MPa时，该减小趋势趋于缓和．液相流动促进气泡的碰撞、合并及迁移是气孔沿熔核周边分布的主要原因．     

Ta1/0Cr18Ni9薄板储能焊熔核高熵化机理

针对钽与钢之间物化性质差异大，焊接时易产生脆性金属间化合物而导致熔焊接头性能低下及裂纹等问题，按照熔核金属高熵化技术思路，利用基于密度泛函理论的热力学第一性原理设计出新型中间层合金Ta₂₀Fe₂₀Ni₂₀Cr₂₀Co₂₀，结合熔合比得到适用于钽/钢储能焊中间层合金成分为Ta₇Ni₃₂Cr₁₉Co₄₂. 采用真空电弧炉熔制纽扣合金锭，继而使用单辊急冷法制备出中间合金箔材，将其用于Ta1/0Cr18Ni9薄板的储能焊连接. 结果表明，在储能焊条件下，Ta1/Ta₇Ni₃₂Cr₁₉Co₄₂/0Cr18Ni9搭接接头形成形貌规则、完整，长径约0.8 mm的扁球形熔核，熔核整体向钢侧发生了偏移. 熔核组织由简单的FCC固溶体组成，无金属间化合物析出，具有典型的高熵合金特征，实现了熔核金属高熵化. 在焊接电压1 000 V，电容500 μF，电极压力30 N下，Ta1/Ta₇Ni₃₂Cr₁₉Co₄₂/0Cr18Ni9储能焊接头平均强度可达到395 MPa.     

Ta1与0Cr18Ni9薄板的储能焊试验

采用电容储能焊方法对Ta1与0Cr18Ni9薄板进行点焊连接,分析了直接点焊与添加高熵中间层的钽/钢接头组织与性能. 结果表明,溶质截流效应可有效抑制快速凝固熔核中脆性金属间化合物产生,实现钽/钢的储能焊接. Ta1/0Cr18Ni9的直接点焊接头中熔化区集中于钢板一侧,呈双曲回转形,熔核中心出现一直径约0.2 mm近圆形气孔,在钽与钢的结合界面处有少量Fe₅Ta₃与Cr₂Ta金属间化合物产生;添加高熵合金中间层的点焊接头,由比较规则的近半扁球状熔核及熔核向基体过渡的熔合区组成,熔核具有简单固溶体结构,组织均匀致密,主要由柱状晶组成. 在相同的参数条件下,钽/钢直接焊接头接头抗剪强度为239 MPa,添加高熵合金中间层的钽/钢接头抗剪强度可达374 MPa.     

Fe-Cu包晶合金急冷箔点焊接头的快速凝固与相分离

应用微型电容储能焊机对厚度约35～45 μm的Fe-60%Cu(质量分数)合金急冷箔进行点焊连接,观察接头的组织形貌,分析接头的冷却速率和温度梯度及其与熔核组织及接头性能的相关性.结果表明:应用电容储能焊瞬间放电所产生的高能量可以实现急冷合金箔的连接,获得直径34 μm、高30 μm、形状较规则的扁球状熔核;接头冷却速率达106 K/s,熔核组织具有明显的快速凝固特征;熔核在快速凝固过程中产生液相分离,富Fe相的小液滴在温度梯度驱动的Marangoni对流作用下向熔核中心移动,并不断凝并长大,最终形成一种第二相向中心偏聚的组织结构;随着温度梯度的增大,富Fe相液滴的运动速度呈线性增大;点焊接头的剪切强度较高,达241 MPa.     

镁合金AZ91D激光熔覆Al_(65)Cu_(20)Fe_(15)涂层的耐腐蚀性

采用6k W横流CO_2激光器在镁合金AZ91D表面激光熔覆准晶Al_(65)Cu_(20)Fe_(15)以提高镁合金表面的性能。结果表明:镁合金表面生成了Al_(65)Cu_(20)Fe_(15)、Al_(12)Fe_(17)、Al_(58)Cu_(44)、AlFe和AlCu。熔覆后试样硬度从70 HV0.2左右提高到145HV0.2。激光熔覆涂层的耐腐蚀性下降。     

粉末冶金Al_1Co_(25)Cr_(18)Fe_(23)Ni_(23)Ta_(10)共晶高熵合金摩擦磨损性能研究

共晶高熵合金因其优异的高温性能有望代替传统的高温结构材料,本研究采用粉末热挤压成形成功制备了Al_1Co_(25)Cr_(18)Fe_(23)Ni_(23)Ta_(10)共晶高熵合金,对比研究了共晶高熵合金显微组织和力学性能,及其在室温和600℃摩擦磨损性能。研究表明:所制备的粉末冶金共晶高熵合金的显微组织由FCC相与Laves相组成,表面能的降低促进Laves相呈等轴晶,提升了合金的高温力学性能。研究温度下,所得共晶高熵合金摩擦过程十分平稳,摩擦因数为0.35,磨损率均在10~(-6)mm~3/(N·m)数量级。共晶高熵合金高温下主要磨损机理为粘着磨损与氧化磨损,高温时共晶高熵合金表面形成了氧化物釉质层,降低了磨损因数与磨损率,提高了合金的耐磨性能。     

具有高非晶形成能力的高熵合金Cu_(29)Zr_(32)Ti_(15)Al_5Ni_(19)（英文）

用铜模吸铸法成功地合成了由2个固溶体相构成的高熵合金(HEA)Cu_(29)Zr_(32)Ti_(15)Al_5Ni_(19)和相同成分的非晶态合金(HE-BMG)。实验结果表明该成分的高熵合金具有高的非晶形成能力。铸态高熵合金Cu_(29)Zr_(32)Ti_(15)Al_5Ni_(19)的抗压强度为1127 MPa。该合金表现出良好的抗回火性能,经750°C处理2 h后,该合金硬度保持在8260 MPa。     

Mechanical properties of Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20 refractory high entropy alloys

Two refractory high entropy alloys with compositions near Nb₂₅Mo₂₅Ta₂₅W₂₅ and V₂₀Nb₂₀Mo₂₀Ta₂₀W₂₀, were produced by vacuum arc-melting. Despite containing many constituents, both alloys had a single-phase body-centered cubic (BCC) structure that remained not only stable after exposure to 1400 °C, but also disordered, as confirmed by the absence of superlattice reflections in neutron diffraction data. Compressive flow properties and microstructure development of these alloys were determined from room temperature up to 1600 °C. Limited compressive plasticity and quasi-cleavage fracture at room temperature suggest that the ductile-to-brittle transition for these alloys occurs above room temperature. At 600 °C and above, both alloys showed extensive compressive plastic strain. The yield stress of both alloys dropped by 30–40% between room temperature and 600 °C, but was relatively insensitive to temperature above 600 °C, comparing favorably with conventional superalloys.     

EFFECTS OF DEFORMATION ON MICROSTRUCTURE AND σ-PHASE FORMATION IN Cr_(25)Ni_(20) STAINLESS STEEL

The microstructure of Cr_(25)Ni_(20)stainless steel under plastic deformation up to 50% has re-vealed an even distributed twins,micro-twins and deformation bands.The σ-phase formationin 800℃ aged specimens is accelerated by its nucleation at either deformation twins orrecrystallized grain boundaries under less or more deformation respectively.In therecrystallized zone,the recrystallization is prior to the precipitation of σ-phase.Althoughrecrystallization may accelerate the formation of σ-phase,it is not essential.The twins andmicro-twins produced by deformation may also provide the additional nucleation sites.     

马氏体转变(二十)

正7.3马氏体的韧性研究材料韧性,易于设想的是位错的塞积。在奥氏体晶体内一滑移面上Frank-Read位错源(简称F-R源)受到切应力τ0,当τ0τp,则位错源启动。形成的位错环先后在晶界处发生塞积,塞积位错数n[131]为     

Resistance spot welding of Ti_(40)Zr_(25)Ni_3Cu_(12)Be_(20) bulk metallic glass:experiments and finite element modeling

The use of resistance spot welding(RSW)technology for joining Ti_(40)Zr_(25)Ni_3Cu_(12)Be_(20) metallic glass was investigated.The microstructure obtained from the welded BMG sample was studied.Joint without precipitates was prepared with welding current of 5.0 kA for 2cycles.A fully coupled thermal-electrical-mechanical finite element model(FEM) was developed to complement the experimental study.The simulated results agree well with the measurements.The effects of key process parameters such as welding current and welding time on the evolvement and microstructure of the weldment were determined and discussed.Moreover,the critical cooling rate for preserving the amorphous state in the weld fusion zone is determined to be approximately 1×10~3 K·s~(-1).     

BSTUDY ON Ni_(25)Ti_(50)Cu_(25) SHAPE MEMORY PARTICLE/Al MATRIX COMPOSITE

ＳＴＵＤＹＯＮＮｉ_（２５）Ｔｉ_（５０）Ｃｕ_（２５）ＳＨＡＰＥＭＥＭＯＲＹＰＡＲＴＩＣＬＥ／ＡｌＭＡＴＲＩＸＣＯＭＰＯＳＩＴＥＬ．Ｓ．Ｃｕｉ；Ｍ．Ｑｉ；Ｐ．Ｓｈｉ；Ｆ．Ｘ．ＣｈｅｎａｎｄＤ．Ｚ．Ｙａｎｇ（ＤｅｐａｒｔｍｅｎｔｏｆＭａｔｅｒｉａｌｓＥ?..     

Soft magnetic Fe25Co25Ni25(B,Si)25 high entropy bulk metallic glasses

New Fe₂₅Co₂₅Ni₂₅(B, Si)₂₅ high entropy bulk metallic glasses (HE-BMGs) with superior soft magnetic and mechanical properties are developed. The HE-BMGs show high glass transition temperature and wide supercooled liquid region (ΔT_x). Fully glassy rods with diameters up to 1.5 mm were fabricated for the Fe₂₅Co₂₅Ni₂₅(B_0.7Si_0.3)₂₅ alloy by copper mold casting method. The HE-BMGs exhibit high yield strength of ∼3624 MPa with large plastic strain of ∼3.1%, which is superior to the pre-developed HE-BMGs. The alloys also possess good soft magnetic properties, i.e., rather high saturation magnetization of ∼0.87 T, low coercive force of ∼1.1 A/m, and high effective permeability at 1 kHz of ∼19,800. This combination of these excellent properties gives the new HE-BMGs good promise for both scientific and engineering applications.     

20tEF-25tLF炉双联工艺试验

采用25tLF炉进行炉外精炼和连铸试验(简称双联),分析了双联试验工艺有关参数与质量的关系.试验结果证明:该工艺是可行的,它不仅保证了钢的质量,提高了生产率,降低了冶炼成本,同时提高了炉体、炉盖、钢包的使用寿命.     

Microstructure and mechanical properties of HVOF sprayed nanocrystalline Cr3C2-25(Ni20Cr) coating

The objectives of this work are to deposit nanocrystalline Cr₃C₂-25(Ni20Cr) powder by thermal spraying and to compare the performance of this coating with that obtained using conventional powder. Towards that purpose, Cr₃C₂-25(Ni20Cr) powders with nanocrystalline grain size and with conventional grain size were deposited using OSU-SJS high-velocity oxyfuel (HVOF) system. The microstructural features, such as morphology of the coated surface, thickness of the coating, the interface of the coating with the substrate, distribution of various phases, and grain sizes etc, were characterized with the help of optical microscope, scanning electron microscope (SEM), and transmission electron microscope (TEM). The amount of oxide phases and pores were determined by means of image analyzer. The presence of various phases was identified by x-ray diffraction (XRD) technique. Hardness, elastic modulus, and indentation toughness were evaluated employing micro indentation technique. The results indicate the presence of three different zones containing only orthorhombic Cr₃C₂ phase, FCC NiCr phase, and mixture of Cr₃C₂ and NiCr phases in, both coatings. The grain sizes in the nanocrystalline coating were in the range of 80 to 100 nm. Nanocrystalline coating exhibits 20% increase in hardness, 40% decrease in surface roughness, and comparable fracture toughness and elastic modulus with respect to conventional coating.     

非晶态Fe_（80）B_（20）合金晶化产物研究

利用Ｘ射线衍射及透射电子显微镜等手段研究了非晶态Ｆｅ_（８０）Ｂ_（２０）合金的晶化产物结构与热处理温度的关系，发现在不同退火温度下晶化产物均由α－Ｆｅ（Ｂ）固溶体和Ｆｅ－Ｂ化合物组成；α－Ｆｅ（Ｂ）固溶体的相对含量随退火温度的升高而增多；化合物有Ｆｅ_３Ｂ和Ｆｅ_（３．５）Ｂ两种，它们的相对含量与退火温度密切相关且表现出不同程度的晶格畸变．