Diffusion-induced Recrystallization Research Articles

Understanding Kirkendall effect in Ni(W) diffusion-induced recrystallization region

This study elucidates the formation of distinct phases, such as intermetallic compounds (IMCs), and the evolution of Kirkendall voids. We not only observed the emergence of polycrystalline IMC layers and distinct diffusion-induced recrystallization (DIR) regions using various experimental methods but also quantified the elusive Kirkendall vacancy fraction by an extended numerical model. Experiments revealed the formation of polycrystalline layers with Ni4W and a distinct DIR region. Irregularly shaped Kirkendall voids were found in the DIR region in the Ni matrix. The observed DIR region thickness exceeding W penetration depth indicated rapid alloying. Experimental data and insights from the Ni-W phase diagram showed exclusive Ni4W formation. EBSD analysis revealed smaller Ni4W grains and larger, irregularly shaped DIR region grains. Quantification of Kirkendall voids through Blob analysis linked numerical results to experiments. Noteworthy findings include the fraction of Kirkendall vacancy and the evolution of the possible vacancy region calculations, highlighting their dependence on the W diffusivity and grain boundary diffusion. Temporal evolution of the vacancy region showed the absence of vacancies near Ni4W/DIR, with the leading edge at DIR/Ni, providing insights into annealing-induced vacancy distribution. This integrated approach enhances understanding of thermodynamics and kinetics in the Ni-W diffusion couple, advancing knowledge crucial for high-temperature materials science applications.

Thermodynamics and kinetics of interdiffusion in Ni//NiAl diffusion couples

The growth behavior of Ni3Al after nucleation at the Ni/NiAl interface was investigated by using macroscopic diffusion couples at low annealing temperatures of 973–1073 K. The thickness and grain size of the Ni3Al phase at different annealing temperatures were statistically analyzed by scanning electron microscopy to evaluate the growth kinetics of the Ni3Al layer. According to the growth rate exponent, the growth of Ni3Al layer to NiAl is almost completely controlled by volume diffusion (VD) when it is above 1023 K, and by boundary diffusion (BD) when it is below 1023 K. In contrast, the growth of Ni3Al into Ni is controlled by VD almost whether at 1023 K or 1073 K. Remarkably, a continuous Al-rich Ni grain layer was formed at the Ni3Al/Ni interface by diffusion-induced recrystallization (DIR), and the experimental results for DIR region of composition and growth behavior were numerically analyzed using the thermodynamic and kinetic models, respectively. The analyses suggest that the composition of the DIR region in the Ni(Al) binary system can be determined by the thermodynamic conditions of the chemical driving force model (CDF model). Additionally, kinetic analysis using the new extended model (NE model) indicates that under current annealing conditions, interface reaction and BD control growth at the moving boundary of the DIR region. Furthermore, the temperature stability range of Ni5Al3 in the Ni//NiAl system was subjected to systematic analysis.

Role of nanostructured Ni surface layer in enhanced Hastelloy alloy diffusion bonding at temperatures far beyond recrystallization

Enhanced Hastelloy alloy diffusion bonding was investigated via introducing nanostructured Ni surface layer. Because the bonding temperature was significantly higher than the nanostructured Ni destabilization temperature, rapidly complete recrystallization and dramatic grain growth occurred. The beneficial effect of high-density short-circuit defects provided by nanocrystalline on enhanced diffusion ought to be limited. However, significantly accelerated diffusion was still observed in the joint. The unique contribution of the nanostructured layer in evolving microstructure is to promote the formation of diffusion-induced recrystallization at the interface, where solute elements could diffuse rapidly along the moving boundaries at a rate several orders of magnitude larger than static grain boundaries. The retained ultrafast atomic diffusion paths result in a bonding temperature of 250 °C–350 °C lower than the conventional diffusion bonding approach. The tensile strength of the achieved joint reached 833 MPa, which was nearly equal to that of the as-delivered substrate.

Diffusion-induced recrystallization during the early stages of solid-state dewetting of Ni-Pt bilayers

We report the phenomenon of diffusion-induced recrystallization (DIR) in the Ni-Pt bilayers deposited on sapphire substrate and annealed at the temperature of 950°C. The as-deposited bilayers were nanocrystalline and exhibited mazed bicrystal microstructure. Short (shorter than 1 min) anneals at 950°C resulted in heterogeneous intermixing, with the isolated intermixed regions containing randomly oriented new grains of varying concentrations being spread in the original bilayer with little intermixing. This intermixing mode was discussed in terms of DIR phenomenon. Further annealing resulted in preferential growth of {111}- and {100}-oriented grains with random in-plane orientations at the expense of the randomly textured matrix formed during DIR, with a clear advantage of the {111}-oriented grains at the later stages of grain growth. Long annealing at the temperature of 1000°C resulted in full solid state dewetting of the bilayer and formation of homogeneous faceted single crystalline Ni-Pt nanoparticles. The majority of nanoparticles exhibited {111} orientation, while a minority of smaller nanoparticles had a {100} orientation. An additional ordering annealing at 550°C reversed the distribution of the particle orientations, with the majority of small nanoparticles exhibiting the (001) orientation and L10 long-range order. These findings demonstrate that the DIR process plays an important role in the diffusion intermixing of Ni-Pt bilayers and in the final geometry of metal nanoparticles formed during solid-state dewetting.

Эволюция структуры и зернограничного ансамбля никеля при диффузионном отжиге в условиях сегрегирующей примеси (серебра) по границам зерен

Investigations of the effect of an impurity (silver) segregating along the grain boundaries of nickel on the evolution of the structure and grain-boundary ensemble under conditions of diffusion annealing at a temperature of 823 K for 6 hours have been carried out. It is shown that, under these conditions, the development of a diffusion-induced recrystallization (DIR) process is observed in the Ni(Ag) system, in contrast to the Ni(Cu) system, in which the process of diffusion-induced grain boundary migration (DIGM) was observed. The estimates made have shown that a possible reason for the fact that diffusion-induced migration of grain boundaries practically does not occur in the Ni(Ag) system can be significantly lower than in the Ni(Cu) system the value of osmotic pressure as the driving force for the DIGM process.

Gallium Liquid Metal Embrittlement of Tin-based Solder Alloys

We report on the embrittlement of tin (Sn)-based solder by liquid gallium (Ga). Exposure to liquid Ga results in a degradation of the intrinsic mechanical properties of the solder due to its ductile-to-brittle transition. Important changes in the solder microstructure accompany this degradation and are predominantly associated with a spontaneous recrystallization of Sn during Ga diffusion into the solder. A detailed investigation of the solder microstructure evolution identifies the recrystallization process as a Continuous Static Recrystallization (C-SRX). Taking into account mechanisms of atomic transport as well as the creation and propagation of defects, a novel liquid metal embrittlement (LME) model is herein proposed, namely the Diffusion-Induced Recrystallization Evolution (DIRE) model.

Diffusion induced recrystallization of Ni3Al-based alloy

The paper represents the study of the kinetics of diffusion-induced recrystallization (DIR) and its effect on the disordering and creep resistance of an alloy based on Ni3Al doped nickel aluminide. Recrystallization was observed in the Ni3Al-based alloy hardened by the particles of chromium carbides at a temperature of 1573 K due to dissolution of carbides and diffusion of chromium in the volume of grains. Recrystallization leads to a sharp decrease in the creep resistance of the alloy due to the formation of an unordered γ phase. The alloy can be used as a heat-resistant material at a temperature of not more than 1500 K.

Effect of sand blasting on oxidation behavior of K38G superalloy at 1000 °C

The impact mechanism of sand blasting on oxidation resistance of K38G superalloys was investigated. Results show that sand blasting influenced little on the oxidation kinetics but suppressed the DIR (diffusion induced recrystallization) process, i.e. keep the original crystal orientation of substrate. Besides, sand blasting refined the crystal size and changed the growing mode of oxide scales by changing the diffusion mechanism, being reflected in the variation in surface morphologies of scales from a feature of piles plus valleys for the polished ones to a feature of flat surface appearance with micrograins for the sand blasted alloys.

Anomalous Kinetics and Regimes of Growth of Intermetallic Phases during Solid State Reactions in Nanosystems

Two interesting features of formation and growth of intermetallic phases in nanoscale solid state reactions will be discussed:Linear-parabolic “normal” growth: it will be summarized that at the very early stages of the growth of an already existing new phase (i.e. when nucleation problems can be neglected) the linear kinetics can be observed due to the so-called diffusion asymmetry. Indeed, it was shown that if the ratio of the diffusion coefficients differ by orders of magnitude in the parent materials (and so also in the new phase), during the growth of a phase bordered by parallel interfaces from the parent phases (normal growth geometry), the shift of the individual interfaces can be linear at the beginning and a transition to the parabolic regime can take place even after a shift of several tens of nanometres. In addition, an AB compound in contact with the pure A and B phases can be dissolved if the diffusion in B is much faster than in either A and AB. This means that the thickness of this phase should decrease, or even can be fully dissolved, at the beginning and only after some time—when the composition in B will be high enough allowing the re-nucleation of this AB phase—will the AB phase grow further.The common problem of two stages of solid state reactions will be revisited: usually the growth can be divided into two stages: a) the formation (nucleation) and lateral growth of the new phases and b) the “normal” growth of the already continuous phase. It was concluded in different previous reviews that in stage b) in the majority of cases the parabolic growth was observed in accordance with the above i) point: the linear-parabolic transition length was typically below 1 μm, which was the lower limit of detection in many previous investigations. On the other hand recently the application of the linear-parabolic growth law for the analysis of experimental data obtained in nanoscale reactions became very popular, not making a clear distinction between a) and b) stages. It will be emphasized here that care should be taken in all cases when the experimental methods applied provide information only about the increase of the amount of the reaction product and there is no information where and how the new phase (s) grow. We have illustrated in a series of low temperature experiments - where the bulk diffusion processes are frozen - that even in this case a full homogeneous phase can be formed by cold homogenization called Grain Boundary Diffusion Induced Solid State Reaction (GBDIREAC). In this case first the reaction starts by grain-boundary (GB) diffusion and nucleation of the new phase at GBs or their triple junctions, then the growth of the new phase happens by the shift of the new interfaces perpendicular to the original GB. This is a process similar to the diffusion induced grain-boundary motion (DIGM) or diffusion induced recrystallization (DIR) phenomena and in this case the interface shift, at least in the first stage of the reaction until the parent phases have been consumed, can be considered constant. This means that the amount of the phase increases linearly with time, giving a plausible explanation for the linear kinetics frequently observed in stage a).

Study of the intermetallic growth in copper-clad aluminum wires after thermal aging

Study of the solid-state diffusion between copper and aluminum was carried out in the temperature range [573–673] K in order to better understand the aging mechanisms which occur in copper-clad aluminum thin wires. A complete microscopic analysis was performed to evaluate the interface composition and corresponding microstructure. The intermetallic phases developed during annealing identified by TEM and X-Ray diffraction analysis are respectively Al2Cu, AlCu, and Al4Cu9. A fine layer containing nanometric copper grains was also depicted and identified as a diffusion-induced recrystallization region. These results agree with EDXS analysis and nanoindentation measurements. The effective heat of formation model was used to evaluate the first phase(s) which happens in the interface and the sequence formation of intermetallic compounds during annealing. This model finely describes the metallurgical aging of copper-clad aluminum wires and explains the presence of only three intermetallic compounds in the interface between copper and aluminum.

On the mechanism of diffusion-induced recrystallization: Comparison between experiment and molecular dynamics simulations

Recent experimental results on diffusion-induced recrystallization (DIR) in size-mismatched thin film metallic diffusion couples are summarized in this paper. As the most striking feature, newly formed grains reveal a preferred concentration which is characteristic for a given couple. Based on a suggested thermoelastic interpretation, stress in front of a migrating grain boundary is calculated from observed characteristic compositions. A remarkable relation between derived stresses and shear strength of respective parent matrix is discovered: plane stress in the diffusion zone amounts consistently to about 80% of the ideal shear strength. To elucidate this relation, molecular dynamics simulations are performed in the copper–gold system applying the embedded-atom method. Simulations indicate a break of coherency within the nanometric diffusion zone when a critical diffusor concentration is reached. Both experiment and simulation show in close agreement that maximum stress in the diffusion zone is of the order of the ideal shear strength and hence far above the yield strength of the material. It is deduced that the limit of coherency controls the observed characteristic concentration levels of DIR.

Diffusion-Induced Recrystallization in Nickel/Palladium Multilayers

Diffusion-Induced Recrystallization (DIR) is investigated in size mismatched thin film interdiffusion couples. New grains formed in the diffusion zone are characterized by distinctive composition levels which seem to be characteristic to the interdiffusing materials. In this paper, we analyzed sputter-deposited Ni/Pd films. The lattice mismatch and the driving force are varied by pre-alloying one side of the diffusion couples. Recrystallization was detected after heat treatment by transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffractometry. We determined characteristic concentrations from XRD data. Remarkably, the difference between the concentration inside newly formed grains and that of the parent layers remains practically constant, when initial layer concentration is varied. Also, the characteristic compositions are nearly independent of temperature. A thermo-mechanic model has been derived, which demonstrates that the observed concentration differences are such that the stress in front of the moving grain boundary reaches a maximum close to the ideal strength of the host material.

Solid-state reactive diffusion between Ni and W

Various alloys are interconnected with W using a Ni intermediate layer by the diffusion bonding (DB) technique. During solid-state heating in the DB technique, however, reactive diffusion occurs at the interconnection between Ni and W. In order to examine the kinetics of the reactive diffusion, sandwich Ni/W/Ni diffusion couples were isothermally annealed at temperatures of T = 1023–1173 K for various times up to t = 366 h. Owing to annealing, Ni 4W is produced as a layer at the Ni/W interface in the diffusion couple and grows predominantly towards Ni. The thickness of the Ni 4W layer increases in proportion to a power function of the annealing time. The exponent of the power function is close to 0.5 at T = 1173 K and gradually decreases with decreasing annealing temperature. Furthermore, grain growth takes place in Ni 4W due to annealing. Therefore, volume diffusion is the rate-controlling process for the growth of Ni 4W at T = 1173 K. At T < 1173 K, however, boundary diffusion contributes to the rate-controlling process, and the contribution of boundary diffusion increases with decreasing annealing temperature. On the other hand, a region alloyed with W is formed in Ni from the Ni 4W/Ni interface by diffusion-induced recrystallization (DIR). The growth rate of the DIR region is much greater than the penetration rate of W into Ni by volume diffusion, and the concentration of W in the DIR region at the Ni 4W/Ni interface is equal to the solubility of W in Ni. Such growth behavior of the DIR region was numerically analyzed using a mathematical model. The analysis indicates that the growth of the DIR region is controlled by the interface reaction at the moving boundary of the DIR region as well as the boundary diffusion along the grain boundaries across the DIR region under the present annealing conditions.

Diffusion-induced recrystallization in nickel/palladium multilayers

In size-mismatched thin film interdiffusion couples diffusion-induced recrystallization (DIR) occurs rather than conventional Fickian atomic transport. Grains formed in this process have characteristic composition levels that are so far not understood. In this work, DIR is studied in sputter-deposited Ni/Pd films. By pre-alloying one side of the diffusion couple, the mismatch, and thus the driving force, are varied. After heat treatment, transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffractometry demonstrate recrystallization. Characteristic concentration levels are derived from X-ray diffraction data. Remarkably, the concentration inside newly formed grains shifts coherently to the concentration inside the parent layers. We demonstrate that the observed concentration levels are in agreement with a recently published thermomechanical model.

Diffusion-induced recrystallization in the Cu(Pd) system at complete solid-solution temperatures

Owing to annealing at complete solid-solution temperatures around 1,000 K, Pd can quickly penetrate into Cu due to diffusion-induced recrystallization (DIR). To examine this penetration behavior, DIR in the Cu(Pd) system was experimentally observed in the present study. A diffusion bonding technique was used to prepare polycrystalline Cu/Pd/Cu diffusion couples. The diffusion couple was isothermally annealed at temperatures of T = 923–1,023 K for various times up to t = 176 h. During annealing, a region alloyed with Pd is produced in Cu from the Cu/Pd interface due to DIR. The concentration of Pd on the Pd-rich side in the DIR region remains almost constant independent of the annealing time but increases with increasing annealing temperature. On the other hand, the mean thickness of the DIR region increases with increasing annealing time. The growth rate of the DIR region is a monotonically increasing function of the annealing temperature. The experimental findings of the kinetics study were quantitatively analyzed using a mathematical model. The analysis satisfactorily reproduces the overall growth behavior of the DIR region.

The hidden link between diffusion-induced recrystallization and ideal strength of metals

Diffusion-induced recrystallization (DIR) is a mechanism which destabilizes thin film multilayers. New grains formed are distinguished by preferred composition levels characteristic for the diffusion couple. By evaluating these concentrations for different material combinations, it is demonstrated that a break of coherency by spontaneous relaxation is the key to understanding the DIR process. Based on this, a thermoelastic model is derived to predict whether DIR can be expected for a given multilayer and to calculate the characteristic concentration levels.

Concentration characteristics of diffusion-induced recrystallization in Cu/CuAu multilayers of varying lattice mismatch

New grains appear in Cu/Au(Cu) thin film interdiffusion couples by diffusion-induced recrystallization. These grains are grouped into different generations of characteristic concentration levels. In this study, the lattice mismatch between initial diffusion partners is systematically varied. It is demonstrated that the intermediate concentrations shift parallel to the concentration of the initial layers. Thus, the characteristic compositions are controlled by the requirement of a characteristic lattice mismatch between parent layer and new grain rather than by metastable phases or highest chemical driving forces.

Concentration Characteristics of Diffusion-Induced Recrystallization

Diffusion-induced recrystallization (DIR) is investigated in Au/Cu and Ag/Pd thin-film interdiffusion couples. It is experimentally demonstrated that several generations of new grains are formed inside the diffusion zone by a cascade-like process. Each generation is distinguished by a characteristic composition level. In order to understand the observed composition levels quantitatively, a thermo-mechanic model has been derived, which determines the thermo-elastic driving force to the grain boundary. By the model, it is shown that those grains dominate the diffusion zone, which develop the maximum possible stress in front of the moving boundary.

Kinetics of Diffusion-Induced Recrystallization in the Cu(Ni) System at Low Temperatures

During annealing at temperatures around 800 K, Ni can quickly penetrate into Cu due to diffusion-induced recrystallization (DIR). To examine this penetration rate, the kinetics of DIR in the Cu(Ni) system was experimentally determined in the present study. Experiments were conducted using polycrystalline Cu/Ni/Cu diffusion couples which were prepared by a diffusion bonding technique. The diffusion couples were isothermally annealed at temperatures of T = 723 K to 823 K for various times up to t = 144 h. During annealing, a region alloyed with Ni is formed in Cu from the Cu/Ni interface due to DIR. The concentration of Ni on the Ni-rich side in the DIR region remains almost constant independent of the annealing time, but gradually increases with increasing annealing temperature. However, the mean thickness of the DIR region increased with increasing annealing time. The growth rate of the DIR region is a monotonically increasing function of the annealing temperature. The experimental findings of the kinetics study were quantitatively analyzed using a mathematical model. The analysis indicates that the growth of the DIR region is controlled by the interface reaction at the moving boundary of the DIR region as well as the boundary diffusion along the grain boundaries across the DIR region.

Orientation Relationship for Fine Grains Formed by Diffusion-Induced Recrystallization in the Ni(Cu) System

In order to examine the crystallography for diffusion-induced recrystallization (DIR) in the Ni(Cu) system, Cu/Ni/Cu diffusion couples were prepared by a diffusion bonding technique from a pure Cu single-crystal specimen and a pure Ni polycrystalline specimen, and then isothermally annealed at a temperature of 923 K for various times of 1–60 h. The Miller indices of the Cu specimen along the Cu/Ni interface are (111). The notation A(B) means that a solute B diffuses into a pure metal A or a binary A–B alloy with the A-rich single-phase microstructure. Due to DIR during annealing, a region with fine grains alloyed with Cu is produced into the Ni specimen from the Cu/Ni interface in the diffusion couple. The orientation relationship between the fine grain in the DIR region and the Cu or Ni specimen was analyzed by an electron backscattered diffraction technique as well as transmission electron microscopy. Orientation relationships close to but not identical to the cube/ cube relationship exist between the Cu specimen and many fine grains in the DIR region. The chemical driving force for the formation of the DIR region, the boundary energy and the boundary diffusion coefficient were evaluated by mathematical models. According to the evaluation, it is likely that fine grains surrounded by small-angle boundaries are formed and grow moderately during DIR. [doi:10.2320/matertrans.MRA2007197]