Grain structure of Ni3Fe alloy

The grain structure of aN ₃Fe polycrystal is studied by means of optical metallography taking into account the type of grain boundaries. Grains with random boundaries having special boundaries on the inside are revealed. Grains are classified by the presence and position of special boundaries. The energy of different types of grain boundaries is estimated. Tomsk State University of Architecture and Building. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 34–42, November 1999.     

Study of the crystallography of slip in the alloy Ni3Al

It has been established that cubic slip is an effective mechanism for the strain of the Ni₃A1 alloy even at room temperature. Traces of cubic slip were observed in an electron microscope for all degrees of strain. The critical spalling stress in the plane of the cube is small and approximately 2.5 kg/mm². In a two-phase alloy consisting of segregations, '-phase (Ni₃Al) and a disordered matrix (-phase), the traces of cubic slip generated in the ordered phase which have reached the phase boundary, are even continued into the segregations of the disordered phase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 7, pp. 42–47, July, 1971.     

Microscopic and mesoscopic structure of pressure-synthesized intermetallic Ni3Al

Optical metallography and transmission diffraction electron microscopy are used to show that the micro- and mesostructure of cast and pressure-synthesized intermetallic Ni₃Al differ considerably. Four types of grains of the major Ni₃Al phase are revealed in the synthesized intermetallide that differ in their domain and dislocation structure. These are single- and polydomain grains with or without dislocations. Institute of Strength Physics and Materials Science, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 53–56, July, 1999.     

Formation of an eutectic structure in Al-Mo-Zr alloy crystallization

A eutectic structure has been obtained in crystallization of an Al-Mo-Zr alloy. This structure is represented by lamellar eutectic colonies, consisting of Mo₃Al₈ and Al₂Zr solid solution, between which more disperse triple and double eutectics with Mo₃Al and Mo₂Zr are crystallized.     

Temperature dependence of the yield point of the alloy Ni3Al

A study was made of the effect of variations in the Ni₃Al composition on the temperature dependence of the yield point. It was found that the yield point has an anomalous rate dependence: the yield point decreases as the rate of strain is increased. From an analysis of these results it is concluded that the anomalous temperature dependence of the yield point of Ni₃Al can be attributed to the same dislocation-retardation mechanisms as are apparently responsible for the anomalous temperature dependence of strain hardening.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 2, pp. 68–74, February, 1971.The authors thank V. Lunev and V. M. Barsanov, students at Tomsk State University, for participation in the experiments.     

耐蚀合金Al3Ni和Ni3Al液态冷凝过程的比较研究

采用F S多体势对液态合金Al3Ni和Ni3Al在不同冷却速度下的微观结构及其转变机制进行了分子动力学模拟 ,得到了不同冷速下各温度的双体分布函数 ;采用HA键型指数法对其结构进行了分析 ,结果表明 :Al3Ni在两种冷速下均以非晶的形式出现 ,只是慢冷时体系的有序度略有升高 ;而Ni3Al的结构及能量转变受冷速影响较大 ,快冷时形成非晶 ,而慢冷时出现明显结晶 ;同样冷速下Al含量较少的Ni3Al体系的有序度高 ,更易形成晶体 ,晶体的形成过程中有能量突变 .     

Why Ni3Al is an itinerant ferromagnet but Ni3Ga is not

Ni3Al and Ni3Ga are closely related materials on opposite sides of a ferromagnetic quantum critical point. The Stoner factor of Ni is virtually the same in both compounds and the density of states is larger in Ni3Ga. Thus in Stoner theory it should be more magnetic, and in local-density approximation (LDA) calculations it is. However, experimentally it is a paramagnet, while Ni3Al is an itinerant ferromagnet. We show that critical spin fluctuations are stronger in Ni3Ga, due to weaker q dependence of the susceptibility, and this effect is enough to reverse the trend. The approach combines LDA calculations with Landau theory and the fluctuation-dissipation theorem using the same momentum cutoff for both compounds. The calculations provide evidence for strong, beyond LDA, spin fluctuations associated with the critical point in both materials, but stronger in Ni3Ga than in Ni3Al.     

Change in the crystallographic structure of grain boundaries in an order-disorder phase transition in Ni3Fe alloy

Electron diffraction microscopy and metallography are used to investigate the crystallographic structure of grain boundaries in Ni₃Fe alloy with short-range and long-range atomic order. It is found that the fraction of special boundaries in alloys with short-range and long-range order is 0.3–0.4. Heat treatment, which leads to ordering, causes a reorientation of some of the grains with boundaries of a general type, boundary migration, and also faceting of some of the boundaries of general type.Tomsk Engineering-Construction Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 3–10, July, 1992.     

Temperature and velocity dependence of mechanical properties of the alloy Ni3Al. III

The temperatures and velocity dependence of the yield point and flow stress of the inter-metallic compound Ni₃Al was studied. It was established that, within the range of temperatures where the anomalous temperature dependence of flow stress is observed, an anomalous velocity dependence of these stresses also occurs. The increase of the yield point and flow stress of the alloy Ni₃Al with the increase of temperature is under the full control of thermally activated mechanisms of hardening. Three stages in the increase of resistance to deformation under increasing temperature were disclosed. It is assumed that two of these are associated with the deposition of atomic defects on sliding dislocations.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 11, pp. 107–113, November, 1971.     

Effect of High Pressures on the Formation of New Compounds in the Al86Ni2Co6Gd6 Alloy

Physics of the Solid State - Using the X-ray diffraction and electron microscopy methods, the structure and the elemental and phase compositions of hypereutectic alloy Al86Ni2Co6Gd6 (hereinafter,...     

合金元素Zr韧化不同计量比Ni3Al合金的微观机制

利用正电子湮没技术(PAT)测量了不同化学计量比二元Ni3Al合金及不同Zr含量Ni3Al合金的正电子寿命谱,并估算了合金基体和晶界缺陷处的自由电子密度.结果表明,二元Ni77Al23合金的基体和缺陷态的自由电子密度都比二元Ni74Al26合金的高.Ni3Al合金晶界缺陷处开空间大于Ni空位或Al空位的开空间,晶界缺陷处的自由电子密度很低,金属键合力很弱.过化学计量比Ni74Al26合金的晶界缺陷开空间比亚化学计量比Ni77Al23合金的大,晶界结合力更弱.这是Ni74Al26合金更脆的原因.在Ni3Al合金中加入Zr,增加了合金中的金属键成分,使基体中的自由电子密度增加,增强了基体金属键合力,同时降低了合金的有序度,使合金晶界容易弛豫,晶界缺陷的开空间变小.另外,Zr原子偏聚到晶界,增加了晶界处的自由电子密度,同时引起晶界处Al贫化,减少了强共价性Ni-Al和Al-Al键,使晶界更易于变形,有利于提高合金的塑性.     

Oxidation of Ni3Al–Ni3Nb alloys

Conclusions The Ni₃Al–Ni₃Nb alloys are oxidized as a result of the diffusion of oxygen ions toward the interface between the alloy and the oxidation product. This diffusion produces a relatively thick inner layer of complex composition; in addition, diffusion of nickel ions toward the interface between the oxidation product and the gas results in the formation of a thin outer layer of NiO. At any temperature, NiO in the inner oxide is reduced to Ni by niobium atoms. During the initial stages of the oxidation, the reduction occurs at the oxide-alloy inter face; during the later stages, it occurs at the interface between the oxide and the suboxide layer. Protective double oxides of NiO · Nb₂O₅ (t = 700–725 °) and NiO · Al₂O₃ (t = 800–850 °) form in the oxidation product. An -Nb₂O₅ conversion occurs at 825–900 ° and considerably reduces the oxidizability of the alloys. The -Nb₂O₅ lattice probably contains fewer oxygen vacancies than the -Nb₂O₅ lattice and thus has better protective properties.Translated from Izvestiya VUZ. Fizika, No. 12, pp. 75–83, December, 1969.     

Grain Structure Formation in Ni3Al Intermetallic Compound Synthesized Under High-Temperature and Pressure Conditions

Russian Physics Journal - The paper presents theoretical and experimental results of studying the grain structure formation of the Ni3Al intermetallic compound produced by self-propagating...     

Structural and phase transformations in a carbide-strengthened alloy based on Ni3Al at high temperatures

A comprehensive study was made of structural and phase transformations in an alloy based on Ni₃Al. It is shown that the aggregate structure formed in the alloy —in which particles of Cr₇C₃ carbides are located preferentially along grain boundaries — block the migration of the carbides. The intensive dissolution of the strengthening carbide phase seen at T 1573 K is accompanied by the formation of two-phase ( + ) boundary regions. These regions are the result of an increase in the concentration of chromium. The method of differential thermal analysis was used to detect the occurrence of an endothermic reaction in the alloy at T>1573 K. This reaction is associated with saturation of the -phase with carbon up to the eutectic concentration and the fusion of the eutectic.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 55–58, March, 1987.     

Study on magnetic property of Fe14Ni86 alloy nanowire array

Ordered Fe₁₄Ni₈₆ alloy nanowire arrays implanted in anodic alumite template (AAT) have been fabricated by electrodepositing the corresponding material into the nanochannels. The wires are 43 nm in diameter and 50 μm in length. Their aspect ratio (ratio of length to diameter) is more than 1000, which results in distinctive magnetic anisotropy. The easy magnetization axis of this system is perpendicular to the membrane. Enhanced coercivity (about 769 Oe) and remanent magnetization up to 70% of the saturation magnetization have been observed. We also studied angular dependent coercivities of the Fe₁₄Ni₈₆ alloy nanowire arrays and found that they fit well with the chain-of-sphere combined model of uniform rotation and non-symmetric fanning.     

Atomistic studies of the structure and composition of grain boundaries in Cu3Au and Ni3Al

In this paper we investigate the atomic structure and composition of grain boundaries in Cu₃Au (weakly ordered compound) and Ni₃Al (strongly ordered compound). Computer simulations employing both the molecular statics and Monte Carlo methods were performed and the Finnis-Sinclair type many-body central force potentials used. First, grain boundaries in stoichiometric alloys are studied with the goal to investigate the impact of ordering strength on the grain boundary structure and composition. In Cu₃Au grain boundaries may become compositionally disordered even at room temperature and the compositional disordering is associated with segregation of gold. In contrast, in Ni₃Al grain boundaries remain compositionally ordered up to very high temperatures. Secondly, the structures of grain boundaries and the effect of Ni and Al segregation in non-stoichiometric Ni₃Al are investigated. Nickel segregation leads to compositional disordering at grain boundaries, while aluminum segregation, which is strongly selective, leads to an ordered grain boundary structure with high Al content. The possible relationship between structural and compositional characteristics of grain boundaries and their mechanical properties, in particular the grain boundary brittleness and its alleviation by additional alloying, are then discussed in the light of the results of this study.     

块体非晶合金 Zr55Cu30Al10Ni5 结构弛豫的研究

应用同步辐射小角x射线散射和差示扫描量热分析对块体非晶合金Zr55Cu30Al10Ni5结构弛豫进行了研究.实验结果表明:经340℃、不同时间退火后的非晶内部的电子密度涨落随退火时间的延长先增大而后减小;玻璃转变温度附近焓弛豫峰的表观激活能则随退火时间的延长先减小而后增大.结果反映了随退火时间的延长,块体非晶合金内部类液体区不断减少及类固体区不断增加的过程.     

High-temperature strength of Ni3Al - Ni3Nb alloys

Conclusions The concentration dependences have been found for the bending and compression strength of Ni₃Al–Ni₃Nb alloys in the temperature range 20–1200 °, and the corresponding dependence for the tensile strength has been found at room temperature. It has been shown that the alloys with 45 and 90 wt.% Ni₃Nb are the strongest. The concentration dependences of the strength of these alloys have been compared with their physical properties.Translated from Izvestiya Vysshlkh Uchebnykh Zavedenii, Fizika, Vol. 12, No. 7, pp. 55–59, July, 1969.