Simulation of Microstructure Evolution of Ni75Al2.9V22.1 Alloy with Progressive Aging Mechanisms

The interrupted aging mechanisms were applied to Ni75Al2.9V22.1 alloy by using the microscopic phase-field simulation method. For the single phase region existing at high temperature, the low content alloy was used as the study object. With the progressive aging mechanisms, the metastable phase γ′ of high temperature can be obtained from the low temperature two phase regions, and the quantity of γ′ phase reduces with increasing temperature. The θ single phase morphology at high temperature regions will turn to be the γ′＋θ two phase morphology at low temperature with the interrupted aging method. Despite of the different precipitation paths of γ′ phase, the precipitation mechanisms are the same for the low temperature aging and high temperature interrupted aging.     

在不同压强下Al75Ti25液态合金结构转变的分子动力学模拟

利用分子动力学研究了液态Al75Ti25合金在不同压强(0GPa、5GPa)下的非晶化能力。通过径向分布函数g(r)、键对、HA和多面体指数分析了Al75Ti25合金体系在不同压强(0GPa、5GPa)下的微观结构随温度的变化关系。结果表明:Al75Ti25合金体系压强分别为5GPa、0GPa时,通过快速冷却液态Al75Ti25合金都能形成非晶态合金;而压强在5GPa时,该合金的非晶化转变温度升高,同时温度降到300K时,表征二十面体的HA指数含量达到8.1%,1551键对的含量为28.5%,因此高压强有助于提高Al75Ti25合金体系的玻璃化转变能力。     

Microscopic Phase-field Simulation of Competition Mechanism Between L12 and D022 Structure in Ni-Cr-Al Alloy

Simulations are performed on temporal evolution of atom morphology and ordering parameters of Ni-14.5 Cr-16.5 Al alloy during early precipitation process at different temperatures based on microscopic phase-field theory; the relationship between precipitation sequence and mechanism of L12 and D022 structure and precipitation temperature are illuminated. The nonstoichiometric ordered L12 phases appear first with congruent ordering＋spinodal decomposition mechanism which is then followed by precipitation of D022 phases at ordering domain boundaries of L12 phases by spinodal decomposition mechanism at 1073 K and 1223 K. The nonstoichiometric L12 phases transform to stoichiometric ordering phases gradually. The incubation period of L12 and D022 phases is shorter at 1073 K than that 1223 K, and growth speed is higher at 1073 K. At 1373 K, L12 and D022 phases appear simultaneously by non-classical nucleation and growth mechanism. After that the particles of D022 phases diminish and disappear gradually; L12 phases grow and single L12 phases are remained at last.     

Microscopic Phase-field Simulation of Competition Mechanism Between Ll_2 and D0_(22) Structure in Ni-Cr-Al Alloy

Simulations are performed on temporal evolution of atom morphology and ordering parameters of Ni-14.5 Cr-16.5 Al alloy during early precipitation process at different temperatures based on microscopic phase-field theory; the relationship between precipitation sequence and mechanism of L12 and D022 structure and precipitation temperature are illuminated. The nonstoichiometric ordered L12 phases appear first with congruent ordering+spinodal decomposition mechanism which is then followed by precipitation of D022 phases at ordering domain boundaries of L12 phases by spinodal decomposition mechanism at 1073 K and 1223 K. The nonstoichiometric Ll2 phases transform to stoichiometric ordering phases gradually. The incubation period of L12 and D022 phases is shorter at 1073 K than that 1223 K, and growth speed is higher at 1073 K. At 1373 K, L12 and D022 phases appear simultaneously by non-classical nucleation and growth mechanism. After that the particles of D022 phases diminish and disappear gradually; L12 phases grow and single L12 phases are remained at last.     

Fe-25Cr-35Ni系合金中的第二相，

采用光学显微镜和扫描电子显微镜以及能谱仪研究了Fe-25Cr-35Ni系合金中的第二相种类和分布。结果表明：Fe-25Cr-35Ni系合金中的第二相主要有3种,即富铌相、氮化物相和碳化物相;其中,富铌相主要沿晶界分布,并且富铌相之间存在成分差异;氮化物相主要为TiN,一般与富铌相共生,其分布主要与氮化物偏析有关;碳化物相数量较多,分布较广泛,晶内、晶界、孪晶界和孪晶内均有分布,经高温固溶处理后可固溶到奥氏体基体中。     

时效制度对Ni20Cr25电热丝膨胀系数的影响

系统研究了时效制度对Ni20Cr25电热丝膨胀系数的影响。结果表明,Ni20Cr25电热丝适宜的固溶处理温度为1150℃;经过930℃+10h时效处理后,由于大量稳定碳化物的析出,电热丝的线膨胀系数明显下降,且显微硬度可达237HV0.01,接近冷拔态的硬度。     

0Cr25Ni7Mo4N双相不锈钢高温热塑性及组织演变

采用热拉伸实验研究了两种不同元素(O、N)含量的双相不锈钢0Cr25Ni7Mo4N在1 000~1 200℃范围内、1s-1应变速率条件下的热变形行为。利用光学显微镜(OM)、扫描电镜(SEM)和透射电镜(TEM)观察并分析了实验钢的组织和夹杂物。结果表明,经铝和硅铁脱氧后的实验钢热塑性良好,而未经脱氧的高O、N含量的实验钢在1 150℃以上才具有良好塑性,故双相不锈钢0Cr25Ni7Mo4N的热加工过程中应该控制温度在1 150℃以上;热加工过程中实验钢以铁素体的动态回复和奥氏体的动态再结晶为主要软化机制;高O、N含量钢中,在相界析出的含铬的氧化物夹杂引起的相界结合强度降低,及高温加工中不恰当的两相比例,是其热塑性较低的主要原因。     

外加应力作用下Ni75Al11.5V13.5合金时效沉淀相的定向粗化

为研究镍基合金Ni75Al11.5V13.5等温时效沉淀颗粒在外应力场作用下的长大,在三元微观相场模型中引入外加应力场,模拟1 046.5 K时效产物L12和D022在外加应力作用下的定向粗化.计算结果表明,微观相场模型可以模拟相结构和晶格中的原子配置,并能清晰地模拟有序相沉淀颗粒间界面.外加应力大小和方向以及持续施加的时间对L12沉淀时效行为有显著影响,施加的外加应力越大、持续时间越长,外加应力方向的定向粗化效应越明显.时效过程中,D022相在L12相与母相界面形核且D022相L12相的间隙中生长,其形态始终受L12相的制约.     

Effect of aging treatment on the microstructures and mechanical properties evolution of 25Cr-20Ni austenitic stainless steel weldments with different Nb contents

The microstructure evolutions and the mechanical properties of the 25Cr-20Ni austenitic stainless steel weld metals with different Nb contents were investigated during the long term aging treatment at 700~?C.M_(23)C_6,Nb(C,N),α-Cr phase and Nb-nitride phase(Z phase)were observed in the microstructures of the aged weld metals.The results showed that theα-Cr phase precipitated in the interdendritic regions of the weld metals after being exposed to~ 700?C for 500 h and the element Nb accelerated the precipitation of theα-Cr phase significantly.The density of theα-Cr phase decreased with the increase of the distance away from the primary Nb(C,N).Additionally,theα-Cr phase showed a crystallographic relationship with the austenitic matrix,■.It was observed that the Z phase precipitated in the periphery of the Nb(C,N)and may replace the Nb(C,N)after long term exposure to high temperature.The transformation of the Nb(C,N)into Z phase suggested that the Z phase had a higher stability than the Nb(C,N)par~ticles at 700?C for long term aging.The tensile strength of the Nb-bearing weld metal showed a continuous decrease at the initial stage of the aging treatment and then went up slightly with the prolonged aging time.However,the elongations and the impact energies of the weld metals decreased monotonously with the increase of the aging time.     

Ga,In对Fe40Ni40P14B6共晶合金非晶形成能力的影响

采用助熔剂净化和铜模铸造相结合的工艺,用工业纯原料制备出块体非晶合金(Fe40Ni40P14B6)100-xGax(x=4～6)和(Fe40Ni40P14B6)100-x-yGaxIny(x=2,4;y=6-x).样品为直径3mm的圆柱体和宽6mm、厚1mm的片材,长度都在20mm左右.研究了Ga,In对Fe40Ni40P14B6共晶合金非晶形成能力的影响.XRD、DSC等分析表明,当x=4～6时,(Fe40Ni40P14B6)100-x(Ga,In)x合金具有强的非晶形成能力.     

Ni_3Al(IC-6)合金防护涂层抗氧化性能研究

Ｎｉ３Ａｌ合金是一种新型高温合金，ＩＣ－６合金是不含Ｃｒ而含１４％Ｍｏ的Ｎｉ３Ａｌ合金。由于高温下Ｍｏ极易氧化升华，因此为使ＩＣ－６合金在高温下可靠工作，需选择ＮｉＣｒＡｌＸ涂层作为ＩＣ－６合金的保护涂层。采用磁控溅射技术，在专用装置上按通过系统研究提出的工艺涂覆ＮｉＣｒＡｌＸ涂层，并对其抗周期氧化性能进行了研究。试验表明：ＮｉＣｒＡｌＹＳｉ涂层对ＩＣ－６合金的防护是非常有效的。     

分子动力学模拟纳米铜晶体中晶界对空穴扩展的影响

用分子动力学方法模拟了∑9对称倾侧晶界铜双晶在拉伸变形过程中晶界对空穴扩展的影响.模拟结果表明:晶界对空穴沿界面的扩展起促进作用,但同时又阻碍空穴越过晶界向另一晶粒扩展;空穴离晶界较远时,晶体在变形过程中表现出比较明显的塑性;空穴的存在会降低晶体的强度,并且空穴离晶界越近晶体强度越低.     

Li(Ni,Co,Mn)O_2合成过程中的结构变化

根据Li(Ni,Co,Mn)O2晶体中Li+和Ni2+的阳离子混排占位模型进行模拟计算,建立了(I003/I104)1/2、(I101/I012)1/2(、I101/I104)1/2等特征衍射线强度比与混排占位参数x的线性方程式。结合实验测得的X-射线衍射谱和混排占位模型研究了Li(Ni,Co,Mn)O2合成过程中的结构演变过程。     

Impact of Arc-Based Welding on the Microstructure Evolution and Mechanical Properties in Newly Developed Cr29.7Co29.7Ni35.4Al4Ti1.2 Multi-Principal Element Alloy

Multi-principal element alloys (MPEAs) have been subjected to extensive research due to their promising potential for numerous applications. Up to now, most of the existing research has been focused on unraveling the microstructural evolution and describing the exceptional performance of these alloys when exposed to demanding environments. Nevertheless, it is especially important to understand their processability so that these advanced engineering alloys can be considered for real-life applications where conventional manufacturing processes, such as welding, are widely used. Herein, gas tungsten arc welding (GTAW) is used for similar welding of a recently developed precipitation-hardened Cr_29.7Co_29.7Ni_35.4Al₄Ti_1.2 MPEA. The microstructural evolution and resulting mechanical properties are characterized by combining optical and electron microscopy, synchrotron X-ray diffraction, microhardness mapping, and tensile testing. The different microstructure features across the welded joint are correlated to the weld thermal cycle and resulting local mechanical properties. Overall, the Cr_29.7Co_29.7Ni_35.4Al₄Ti_1.2 MPEA exhibits excellent weldability and mechanical properties, reaching a tensile strength of ≈750 MPa and a fracture strain of ≈33% during tensile tests, making this alloy viable for structural applications. The innovative aspect of this work includes the expansion of the current understanding on the physical metallurgy of MPEAs, as well as the examination of this particular MPEA's processability.