Diffusion of platinum, vanadium and manganese in Ni3Al phase under high pressure

Diffusion of platinum, vanadium, and manganese in the Ni₃Al phase is investigated under high pressure. Platinum atoms occupy cubic face centred sites (α) in the L1₂ ordering structure. Vanadium atoms occupy cubic corner sites (β). Manganese atoms occupy both sites. Activation volumes ΔV for diffusion of these diffusing atoms to the molar volume of the Ni₃Al phase V₀ are as follows:

Diffusion of Hydrogen along the Grain Boundaries in Ni3Al Alloys

The diffusivity of hydrogen in two Ni3Al alloys (No.1 and No.2) has been measured in the temperature range of 100℃ to 420℃ using an ultrahigh vacuum gaseous permeation technique. The diffusivity data fall into two segments, in which the hydrogen diffusivity adheres to the Arrhenius form, respectively. From the hydrogen diffusivity, it is conjectured that the hydrogen diffusivity reflects the hydrogen transportation along the grain boundaries at lower temperature and the hydrogen transportation in the lattice at higher temperature. The intergranular fracture of Lit-type intermetallics induced by hydrogen at relative low temperature results from hydrogen transportation along the grain boundaries and not in the lattice.     

Nanostructured Ni3Al layers and Ni3Al/Ni multilayers obtained by magnetron sputtering

Intermetallic Ni₃Al thin layers and Ni₃Al/Ni multilayers were deposited on a Si wafer by means of magnetron sputtering. The structure and morphology of the layers have been characterized by X-ray diffraction, transmission electron microscopy and atomic force microscopy. The polycrystalline films are textured in the (111) direction and have grain sizes below 20 nm. Superlattice reflections due to chemical order have been observed in the electron microscope. It is shown by x-ray diffraction that the multilayers grow coherently on the amorphous substrate.     

Diffusion bonding of TiAl using Ni/Al multilayers

With the stimulus of temperature and pressure Ni and Al can quickly react and produce the intermetallic compound NiAl. This reaction is highly exothermic and high temperatures can be attained in the surroundings. These characteristics make Ni/Al multilayers very attractive to technological applications as localised heat sources. In this study, Ni/Al multilayer thin films are used to promote bonding between TiAl intermetallic alloys. Ni and Al alternated nanolayers were deposited by d.c. magnetron sputtering onto TiAl samples, with periods of 5, 14 and 30 nm. Joining experiments were performed at 900 °C for 60 or 30 min, in a vertical furnace with a vacuum level better than 10⁻² Pa. Applied pressures of 5 MPa were tested. The microstructure of the cross-sections of the bond interface was analysed by energy dispersive X-ray spectroscopy and characterised by scanning electron microscopy. The observation of the microstructure for 14 and 30 nm period multilayers revealed sound bonding, while for 5 nm period porosity and cracks within the interlayer thin film were observed. The interface is divided into three distinct zones: one with columnar grains, another with very small equiaxed grains and the third with larger equiaxed grains. The joining process appears to depend on the diffusion of Ni and Ti across the interface and is assisted by the nucleation of nanometric grains at the interface. The mechanical strength of the joints was evaluated by shear tests. The bonds produced at 900 °C/5 MPa/60 min/14 nm exhibited the highest shear strength of 314 MPa.     

Zirconium-Induced Softening in Hyperstoichiometric Ni3Al

The room temperature compressive properties and microhardness of Ni3AI alloys doped with Zr were studied. For the hypostoichiometric Ni3AI alloys, the compressive strength and microhardness increased with an increase in Zr content, while softening behavior induced by doping with a certain amount of Zr was observed in hyperstoichiometric Ni3AI alloy. Possible mechanisms for the softening effect were suggested.     

Alloy softening in Ni3Al polycrystals

The alloying effect of boron on localized deformation in Ni₃Al polycrystals containing 24–26 at% AI was studied using microhardness indentation. Alloy softening was observed both along the grain boundaries and in the grain interior. The softening effect decreased as the aluminium concentration increased. For alloys of near-stoichiometric composition, the maximum effect occurred at about 0.23 at% (500 wt p.p.m.) boron. A softening mechanism based on cross slip of screw dislocations was proposed.     

Ni3Al复合材料的生产工艺

介绍了ＮｉＡｌ复合材料的主要工艺和增强相的分类,液相工艺主要包括熔铸法,反应烧结和热等静压、反应熔渗ＳＨＳ工艺以及喷射成形等方法。固相工艺介绍了热压、热等静压和机械合金化,分析了各种工艺的优缺点。     

Ordering and structural transformations in Ni3Al alloys

X-ray diffraction profile studies on the filings of stoichiometric and off-stoichiometric compositions of Ni₃Al alloys, with and without boron additions, were conducted to clarify some of the significant anomalies noticed in the literature. The long-range order parameter was estimated as a function of temperature in all the four alloys from (1 0 0)/(2 0 0) and (1 1 0)/(2 2 0) pairs of reflections. The L1₂ structure appears to attain a maximum stability at about 600 °C, around which temperature its order parameter was close to the theoretical value. Above 600 °C, this structure becomes less stable and there appears to be formation of an additional structure of a lower symmetry. Also in the Materials Science Section, Faculty of Mechanical Engineering, University of Twente, Enschede, The Netherlands.     

Annealing studies of cold-rolled Ni3Al

Annealing studies of cold-rolled Ni₃Al established that the recrystallization kinetics obey the Avrami equation and that the grain-growth kinetics obey the relation ¯d=Ct ⁿ where ¯d is the average grain size, t the time and C and n are parameters whose magnitude depends on temperature. Disorder is introduced during deformation but subsequently removed during recrystallization. Antiphase boundaries are found in some recrystallized grains but do not show any preference to lie on {100} planes, contrary to predictions based on Flinn's nearest-neighbour approximation model. Twins, dislocation networks an planar faults are also found in recrystallized grains.     

Uniting Strength and Toughness of Al Matrix Composites with Coordinated Al3Ni and Al3Ti Reinforcements

Hybrid aluminum composites are fabricated in a novel manner to characteristically induce a layer‐wise aligned distribution of micro‐scale Al₃Ni and Al₃Ti intermetallic particles that are formed in situ within a ductile Al matrix. The simple and unique Rolling of Randomly Orientated Layer‐wise Materials (RROLM) manufacturing methodology enables microstructural tailoring of the intermetallic reinforcing particles to prescribe enhanced crack tip deflection caused by the complex interaction of local veins of reinforcement particles, in an effort to overshadow the classical loss of toughness in large‐particle reinforced composites. The complimentary reinforcements and their interface with the Al matrix are revealed to have a gradual transition zone that functions to maintain critical cohesion with the particles and the matrix, empowering the superior load transfer capability of the particles, and reducing microvoid penetration into the matrix. In situ three‐point bending observations combined with a local strain field analysis, demonstrate the distinctive crack deflection mechanisms exhibit by the composite. Deviating from the norm, this specialized particle reinforced composite exhibited both strengthening and toughening mechanisms simultaneously, over control samples. The investigated design strategy and model material will assist materials development toward light‐weight, stronger, and tougher particle reinforced Al matrix composites.     

Deformation behaviour of recrystallized Ni3Al

Deformation behaviour of the recrystallized Ni₃AI with non-stoichiometric and stoichiometric compositions have been investigated. Recrystallization microstructures in non-stoichiometric Ni₃AI are composed of the Ll₂ ordered and a small amount of the f c c disordered . It is shown that the large elongation of non-stoichiometric Ni₃AI is due to -phase existing at recrystallized t'- grain boundaries. Recrystallization microstructures in stoichiometric Ni₃AI are confirmed to be a single phase of . Coarse-grained stoichiometric Ni₃AI shows considerable ductility, although the fine-grained compound is brittle. The ductility may be related to the low yield strength in the coarse-grained samples.     

Diffusion Bonding of Ti_3Al Base Alloy

: The effects of diffusion bonding temperature and holding time on the joint strength of Ti3Al base alloy has been investigated in this paper. The shear strength of Ti-14Al-21Nb-3Mo-V alloy diffusion bonding joint under pressure of 12 MPa at 990℃ for 70 min was obtained to 797.6 MPa which approaches the base material strength. In addition, a short-time diffosion bonding process was studied in order to decrease the bonding cost. With the deformation of the specimens of 2.5% and the bonding temperature of 990℃ for 15 min, the bonding strength could reach 801 MPa.