Microscopic phase-field simulation of Cr atom substitution character during formation of Ll2 and DO22 phases in Ni-Cr-Al alloy

The simulations of Cr atom substitution character during the formation of L12 and DO22 phases in Ni-Cr-Al alloy were performed at 873 K based on microscopic phase-field model. It is found that the substitution of Cr is affected by Cr and Al contents and limits of occupation probabilities of Cr atom in L12 phase are present. The precipitate is single L12 phase when the component is less than the limit, Cr atoms substitute the Al sublattices in Ll2 phase, and both of atoms Al and Cr occupy the β-sites and complex phases Ni3（Al1-xCrx） are formed; Cr atoms enter Ni sites when Al and Cr contents exceed the limit, and substitute β-sites or both of α- and β-sites. The DO22 phase is formed at the boundary of Ll2 phase.     

Microscopic phase-field simulation for coarsening behavior of L12 and DO22 phases of Ni75CrxAl25-x alloy

Based on the microscopic phase-field dynamic model and the microetasticity theory, the coarsening behavior of L12 and DO22 phases in Ni75CrxAl25-x alloy was simulated. The results show that the initial irregular shaped, randomly distributed L12 and DO22 phases are gradually transformed into cuboidal shape with round comer, regularly aligned along directions [100] and [001], and highly preferential selected microstructure is formed during the later stage of precipitation. The elastic field produced by the lattice mismatch between the coherent precipitates and the matrix has a strong influence on the coarsening kinetics, and there is no linear relationship between the cube of the average size of precipitates and the aging time, which does not agree with the results predicted by the classical Lifshitz-Slyozov-Wagner. The coarsening processes of L12 and DO22 phases are retarded in elastically constrained system. In the concurrent system of L12 and DO22 phases, there are two types of coarsening modes: the migration of antiphase domain boundaries and the interphase Ostwald ripening.     

A2B7型La0.75Mg0.25Ni3.5-xCrx(x=0～0.3)贮氢合金相结构及电化学性能研究

采用感应熔炼方法制备了La0.75Mg0.25Ni3.5-xCrx(x=0,0.05,0.1,0.2,0.3)四元贮氢合金,系统地研究了合金B端Cr元素对Ni部分替代对合金相结构及电化学性能的影响.X衍射(XRD)分析表明,La0.75Mg0.25Ni3.5合金是由La2Ni7相组成.随着Cr元素的加入,该类合金中出现LaNi5相及LaNi3相,且随着Cr含量的增加而增多.电化学测试表明,随Cr含量的增加,合金电极活化次数变化不大,最大放电容量逐步降低,合金的最大放电容量由x=0.05时的383.43 mAh/g下降到x=0.3时的348.40 mAh/g;而合金的高倍率放电性能呈现先增后减的趋势,当电流密度为900 mA/g时,合金的高倍率放电性能由83.66%(x=0)增加到92.57%(x=0.05)然后减小到83.9%(x=0.3);循环稳定性先增加后下降,当x=0.1时合金电极的循环寿命达到最大(S100=74.71%).     

不锈钢厂电弧炉粉尘中含铬相的形成

采用SEM-EDS和XPS对粉尘的微观结构和表面元素分布分别进行了检测,然后用FACTSage 5.2软件通过热力学平衡计算研究了Cr-Fe-Zn-Mn-Mg-Al-Ca-Ni-O-Cl体系在尾气管中的演变行为,以及温度、氧气含量和粉尘中碱金属元素等对Cr-O2系统的影响.结果表明,计算结果和实验结果基本吻合.在Cr-O2体系中,Cr元素主要以Cr2O3形式稳定存在.在高温区均有少量的CrO3或CrO2生成,并且随着温度的升高,含量不断增加.在尾气系统中,氧势越高或者含氧量越多,越容易在高温区生成CrO3.在氧化性气氛中,碱金属的存在易于与Cr结合形成含Cr（Ⅵ）物相,如K2CrO4和Na2CrO4.     

Microstructures of spinodal phases in Cu-15Ni-8Sn alloy

The microstructures of spinodal phases in Cu-15Ni-8Sn alloy were studied by TEM. It was found that when the alloy is completely in a as-quenched state, spinodal decomposition is quick. Ordering appears after spinodal decomposition. The ordered phase with DO22 structure has three variants obtained from coarsening spinodal structure. The reason of ordering appeared after spinodal decomposition is that the content of solute atoms needed by ordering is higher than the average, which can be reached by the composition fluctuation of spinodal decomposition. It was speculated that the morphology of the ordered phase is needle-like.     

相图热力学计算在新型钴基高温合金设计中的应用

利用CALPHAD方法建立了Co—M—Al—W—Cr新型钴基高温合金热力学数据库,阐述了相图热力学在指导合金设计中的作用,并应用该数据库预测了Co—M—W—Cr四元系合金和Co-M-Al-W-Cr五元系合金的相平衡关系,分析了Ni含量对Co—Al-W基高温合金γ／γ’相平衡的影响,进一步证明热力学数据库将为开发新型钻基高温合金提供理论支撑．     

Structure and migration characteristic of heterointerfaces during the phase transformation from L1<Subscript>2</Subscript> to DO<Subscript>22</Subscript> phase

Based on the microscopic phase-field model, the structure and migration characteristic of ordered domain interfaces formed between DO₂₂ and L1₂ phase are investigated, and the atomistic mechanism of phase transformation from L1₂ (Ni₃Al) to DO₂₂ (Ni₃V) in Ni₇₅Al _x V_25−x alloys are explored, using the simulated microstructure evolution pictures and the occupation probability evolution of alloy elements at the interface. The results show that five kinds of heterointerfaces are formed between DO₂₂ and L1₂ phase and four of them can migrate during the phase transformation from L1₂ to DO₂₂ except the interface (002)_D//(001)_L. The structure of interface (100)_D//(200)_L and interface (100)_D//(200)_L·1/2[001] remain the same before and after migration, while the interface (002)_D//(002)_L is formed after the migration of interface (002)_D//(002)_L·1/2[100] and vice versa. These two kinds of interface appear alternatively. The jump and substitute of atoms selects the optimization way to induce the migration of interface during the phase transformation, and the number of atoms needing to jump during the migration is the least among all of the possible atom jump modes.     

STURCTURAL CHARACTERISTICS AND QUANTUM CHEMISTRY CALCULATION OF Al-DOPED BORON CARBIDES

Structural characteristics, chemical bonds and thermoelectric properties of Al-doped boron carbides are studied through calculations of various structural unit models by using a self-consistent-field discrete variation X. method. The calculations show that Al atom doped in boron carbide is in preference to substituting B or C atoms on the end of boron carbide chain, and then may occupy interstitial sites, but it is difficult for Al to substitute B or C atom in the centers of the chain or in the icosahedra. A representative structural unit containing an Al atom is [C—B—Al]~(ε )—[B_(11)C]~(ε-), while the structural unit without Al is [C—B—B(C)]~('-)—[B_(11)C]~(' ), and the coexistence of these two different structural units makes the electrical conductivity increased. As the covalent bond of Al—B or Al—C is weaker than that of B—B or B—C, the thermal conductivity decreases when Al is added into boron carbides. With the electrical conductivity increasing and the thermal conductivit y decreases,     

Phase Evolution and Oxidation Resistance of YSZ/(Ni,Al) Composite Coatings in CH<Subscript>4</Subscript> Atmosphere

YSZ/(Ni, Al) composite coatings with different Ni:Al mole ratios were deposited on superalloy Inconel 600 by electrophoretic deposition (EPD) technique, followed by sintering in CH₄ atmosphere at 1 100 °C for 2 h and isothermally oxidation at 1000 °C for 50 h. After sintering at 1100 °C for 2 h in CH₄ atmosphere, besides ZrC and t-ZrO₂ phases, the phase constitutes of Ni:Al mole ratios with 1:3, 1:2, and 1:1 were (Zr, Al)C, AlNi₃ and Ni phases, respectively. A remarkable difference in the oxidation behaviors of YSZ/(Ni, Al) composite coatings with different Ni:Al mole ratios was observed. For YSZ(Ni:Al=1:3) coated sample, oxidation at 1000 °C causes decomposition of the (Zr,Al)C solid solution to metallic Al, and then most of the Al is oxidized to Al₂O₃. For the YSZ(Ni:Al=1:2) coated sample, oxidation at 1000 °C mainly causes decomposition of the AlNi₃ phase. For YSZ(Ni:Al=1:1) coated sample, after oxidation at 1000 °C, most of the Ni is oxidized to NiO phase, and tolerated 50 h of oxidation and finally cracked and spalled from the specimen. YSZ(Ni:Al=1:3) and YSZ(Ni:Al=1:2) coated samples show superior oxidation resistance than that of YSZ coating. The different oxidation resistance mechanisms of YSZ/(Ni, Al) composite coatings sintered in CH₄ atmosphere were discussed.     

稀土和铝对穿孔顶头钢高温机械性能的影响

研究了穿孔顶头常用钢２５Ｃｒ２Ｎｉ４ＷＡ钢经ＲＥ（稀土）和ＲＥ＋Ａｌ两种合金化工艺后其高温强度和硬度的变化。试验结果与分析表明，单一ＲＥ合金化对高温强度有所提高，但使高温硬度下降；ＲＥ＋Ａｌ合金化对高温强度及硬度均有较大提高，从而可减少穿孔顶头的塌鼻、粘钢现象。由于ＲＥ＋Ａｌ合金化工艺实用且成本不高，可望大力推广应用。     

Alignment of primary Al<Subscript>3</Subscript>Ni phases in hypereutectic Al-Ni alloys with various compositions under high magnetic fields

Al-Ni hypereutectic alloys with various compositions were solidified under various magnetic field con- ditions to investigate the alignment of primary Al3Ni phases. The results showed that the application of high magnetic fields could improve the homogeneity of the primary Al3Ni phase distribution and induce the alignment of primary Al3Ni phases in the direction perpendicular to the magnetic field direction to form chain-like structures. However, the alignment was different from the orientation of the Al3Ni...     

热喷涂涂层与电镀层的结合与界面

为提高热喷涂涂层与电铸层间的结合强度,分别选用QAl9-2、Ni95Al5和0Cr25Al5等3种自结合材料做过渡层,沉积在电弧喷涂3Cr13涂层与电铸Ni层之间.结果表明,Ni95Al5过渡层的效果最好,可提高涂层体系结合强度至少一倍,QAl9-2与0Cr25Al5过渡层的效果次之.借助于扫描电子显微镜,分析了热喷涂涂层与电铸层界面的微观组织,研究了过渡层的强化机制.在该涂层体系中,自结合涂层与电铸镍层发生冶金结合,自结合涂层的自由表面为后续沉积的3Cr13涂层提供了极好的机械结合界面,保证了涂层体系的可靠结合.     

Kinetics of Combustion Synthesis in Ti-C-3Ni-Al System

The Kinetics and mechanisms of the combustion reaction in theTi-C-3Ni-Al system were studied. Samples were prepared by igniting compacts of elemental Ti, C, Ni and Al powders with a heating tungsten coil under an inert argon atmosphere. The activation energies of Ti+C+50wt%(3Ni+Al)→TiC+50%Ni3Al and Ti+C+80wt%(3Ni+Al) →TiC+80%Ni3Al exothermic reactions were determined by measuring the combustion wave velocity and the combustion temperature, which are 129kJ.mol-1 and 79kJ*mol-1, respectively. The mechanism of formation of products for Ti-C-3Ni-Al system was found:metal phases (Ti-3Ni-Al) are melted in combustion process,and carbon dissolves into the liquid metal and TiC is subsequently precipitated out of solution, and Ni3Al is crystallized during the cooling process. The mechanism is fairly similar with that of Ti+C→TiC and Ti+C+Ni→TiC+Ni. There are two reactions (Ti+C→TiC, 3Ni+Al→Ni3Al) in the Ti+C+3Ni+Al system, and the wave velocity is mainly controlled by the velocity of Ti + C→TiC, but the velosity of 3Ni+Al→Ni3Al may play a significant role when Ni3Al contents are higher than 70wt%.     

18Cr_2Ni_4WA钢中的C—Cr,C—Ni,C—W偏聚对固态相变的影响

从“余氏理论”出发.对18Cr_2Ni_4WA钢的价电子结构进行了计算,应用“固溶液微观不均匀性理论”,在构成材料原子的价电子结构的深度上,提出了C—Cr,C—Ni,C—W偏聚,并讨论了这种偏聚对18Cr_2Ni_4WA钢的相变动力学与组织的形态的影响。     

Al-Al2O3-铁磁金属隧道结界面的表征

用梯形势垒模型计算偏置Al Al2 O3 铁磁金属 (Fe ,Co ,Ni和Ni80 Fe2 0 )隧道结的I V曲线 ,通过与结在 77K温度下的实验I V曲线拟合决定了结的势垒参数 .拟合结果表明 ,对于上电极为不同铁磁金属的 4种结 ,Al Al2 O3 界面处的势垒高度差别很小 ,而Al2 O3 Fe ( Co , Ni, Ni80 Fe2 0 )界面处的势垒高度以及势垒宽度则分别为 1 72eV ,1 76eV ,1 86eV ,1 6 9eV以及 1 7 6 0 ,1 1 2 2 ,1 2 2 8 ,1 3 4 0 .势垒高度和宽度因铁磁金属上电极不同而改变的现象可归因为铁磁金属原子向Al2 O3 势垒层渗透 ,以及在界面区域铁磁金属原子与Al2 O3 的氧化反应导致附加氧化势垒层的形成 .     

无镍含氮18Cr奥氏体不锈钢中相平衡的热力学计算

利用ThermoCalc软件和相关数据库对不同Mn含量（质量分数,以下均同）及添加少量（质量分数,以下均同）Mo和C时,Fe-18Cr-Mn-Mo-C-N合金系在压力为100 kPa条件下随N含量（质量分数,以下均同）变化的垂直截面相图进行了计算.结果发现,当不添加Mo和C时,Mn含量从0增加到12%时,γ/（α＋γ）相边界向左侧移动;随着Mn含量的继续增加,γ/（α＋γ）相边界又向右侧移动.γ/（Cr2N＋γ）、γ/（σ＋γ）和γ/（N2＋γ）相边界一直向右侧移动.γ/（Cr2N＋γ＋gas）相平衡时的γ相中氮含量随着Mn的添加也逐渐增加,即由0%Mn时的0.85%N变为22%Mn时的1.69%N,N在γ相中的固溶度提高近一倍.在18%Mn的合金中含有0.02%C时,奥氏体区的范围没有发生明显的变化,但存在M23C6化合物;当继续添加2%Mo时,γ/（α＋γ）相边界向右侧移动,而且不但存在M23C6化合物还有M6C化合物.Fe-18Cr-18Mn-0.5N钢的奥氏体化温度及Cr2N相析出温度与此合金系的热力学计算结果基本一致,表明这些计算结果对Fe-18Cr-Mn-Mo-C-N合金系的成分设计及热处理工艺有重要参考价值.     

镍离子注入Al2O3/1Cr18Ni9Ti钎焊界面成分分析

利用扫描电镜观察了镍离子注入Ａｌ２Ｏ３／１Ｃｒ１８Ｎｉ９Ｔｉ钎焊界面的形貌,并用ｘｌⅡ能谱分析仪对焊缝进行面、线和点扫描成分分析,结果表明,焊接面非常完整,在Ａｌ２Ｏ钎焊料／１Ｃｒ１８Ｎｉ９Ｔｉ相互界面处存在着元素扩散。     

激光重熔制备TA1表面Ni/Al复合抗高温氧化涂层

为了提高纯钛的高温抗氧化性能,采用电弧喷涂和等离子喷涂方法在纯钛表面制备Ni/Al复合涂层.利用激光重熔使得Ni层与Al层发生冶金反应,对试件进行800℃×40 h连续氧化.根据生成的金属间化合物特征研究纯钛的高温抗氧化行为.结果表明,经过表面改性处理后Ni/Al复合涂层可以显著提高纯钛的高温抗氧化性能.在激光重熔过程中Ni/Al复合涂层中的Al发生熔化扩散并与Ni形成以Ni₂Al₃相为主的扩散层.在氧化过程中Ni/Al复合涂层表面形成连续且致密的α-Al₂O₃氧化膜与大量NiAl相,表面扩散层中的富铝相可为表面提供充足的Al元素,进而对纯钛基体提供有效的高温抗氧化保护作用.     

过共品铸造Al-Si—Cu—Mg—Fe合金组织性能研究

通过正交试验和单因素试验,考察了Cu、Mg、Zn、Ni和Fe对Al—18Si过共晶铝硅合金室温及高温（350℃）力学性能的影响规律,利用光学金相显微镜（OM）、扫描电镜（SEM）、能谱分析仪（EDX）对合金中富Cu相、富Fe相的组织组成进行了分析．结果表明：Cu、Mg是提高AI-18Si过共晶铝硅舍金室温及高温强度的主要因素;Zn含量增加明显降低合金350℃时的高温强度,改善合金的室温和高温延伸率;Fe降低合金的室温强度,显著提高合金的高温强度;当Cr：Fe=0．35：1,Mn：Cr=2：1,含铁0．8％～1．2％时,Al-18Si-4．0Cu-0．7Mg-0．2Zn-1.0Ni-（0．8～1．2）Fe合金力学性能σb（25℃））310MPa,延伸率受（25℃）≥0．75%,σb（350℃）〉130MPa,延伸率δs（35℃）〉1．5％;合金中富铜相主要以块状Al。Cu相和白灰色花卉状A15Si。cu2Mg8相存在,富铁相主要以三叶草状、树枝状和棒状Al5Si（Cr,Mn,Fe）相存在．     

Behavior of NiCrAIY coating on the TC6 titanium alloy

A NiCrAlY coating was deposited on the TC6 titanium substrate by arc ion plating (AIP). The structure and morphologies of the NiCrAlY coating were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the influence of vacuum heat treatment on the element diffusion behavior was studied. The results showed that the γ'-Ni3Al phase was precipitated on the NiCrAlY coating after heat treatment. The Ni3(Al,Ti), TiNi, and Ti2Ni intermetallic layers appeared at the interface from the outside to the inside at 700°C, and the thickness of the intermetallic layers increased with the increase in temperature. At 700°C Ti and Ni were the major diffusion elements, and the diffusion of Cr was observed when the heat treatment temperature increased up to 870°C. The violent inward diffusion of Ni at 950°C resulted in the degradation of the NiCrAlY coating.