Solid-state Diffusion Mechanism Research Articles

Ag–(In–Bi) solid-state bonding

Solid-state diffusion bonding is a metallurgical technique to bond interfaces. We identify Ag–(In–Bi) as a material system that can be bonded at 65 °C. This work aims to demonstrate low-temperature bonding and to determine if Bi precipitates form through a solid-state diffusion mechanism. Bonds were formed at 65 °C utilizing a 78.5-at% In–Bi eutectic foil and a 95-at% In–Bi foil, with bonding times 1, 2, 4, and 8 days. These foils were sandwiched between two pieces of Ag, forming an Ag/In–Bi foil/Ag bonding stack. Thanks to bridging of AgIn2, a temperature stability of ~166 °C is possible. Using a bonding material with higher In content (in our case 95 at% In) than the eutectic did not reduce the growth rate of AgIn2. The BiIn2 left over from the reaction was surrounded by the growth of AgIn2. The solid-state bonding results presented in this paper indicate that dissolution is a necessary condition for the unique Bi precipitates previously seen in the Ag–(In–Bi) solid–liquid system.

A new mode of mineral replacement reactions involving the synergy between fluid-induced solid-state diffusion and dissolution-reprecipitation: A case study of the replacement of bornite by copper sulfides

Mineral replacement reactions are one of the most important phenomena controlling the geochemical cycle of elements on Earth. In the early years, solid-state diffusion was proposed as the main mechanism for mineral replacement reactions, but over the past 20 years the importance of the coupled dissolution-reprecipitation (CDR) mechanism has been recognized. In the presence of a fluid phase and at low temperatures (e.g., <300 °C), CDR is the predominant mineral replacement process compared to relatively slow solid-state diffusion. However, in the present case study, we show that the rate of solid-state diffusion is comparable to the rate of CDR processes during the replacement of bornite (Cu5FeS4) by copper sulfides at 160–200 °C. The experiments initially produced chalcopyrite lamellae homogeneously distributed in the entire bornite grain, and each lamella was enveloped by digenite. The lamellae were formed by removing Fe3+ from bornite via solid-state diffusion, since there was no evidence for fluid entering the bornite grains during lamellae formation. An interesting discovery is that solid-state exsolution of chalcopyrite lamellae was induced by the bulk hydrothermal fluids surrounding the mineral grains, because in the absence of fluids under otherwise identical conditions, no exsolution occurred, and because the exsolution rate and lamellae size were sensitive to the composition of hydrothermal fluids. We hypothesize that this fluid-induced solid-state diffusion (FI-SSD) mechanism is made possible by the similar topology of the crystal structure of these phases. The solid-state diffusion of Fe3+ within bornite and across the resultant chalcopyrite and digenite phase boundaries is facilitated by the near-identical S framework. Parallel to and after lamellae exsolution, CDR reactions proceeded from the surface to the interior of the grains or along fractures, replacing chalcopyrite by digenite, and digenite by covellite and/or chalcocite, depending on experimental conditions. The synergy between FI-SSD and CDR resulted in complex reaction pathways for reactions in five acidic hydrothermal fluids with or without added Cu2+, Cu+, Cl−, SO42−, and SO32−. The outcomes of these experiments imply that (1) under conditions where cation diffusion rates are of the same order of magnitude as dissolution and precipitation rates, hydrothermal fluids can induce and control solid-state diffusion processes, e.g., exsolution; (2) mineral replacement can be a result of the synergy between FI-SSD and CDR mechanisms; this happens at low temperatures (≤200 °C) in chalcogenide systems, but could affect silicate and oxide systems at amphibolite to granulite to eclogitic metamorphic grade; and (3) the synergy between FI-SSD and CDR mechanisms can lead to complex reaction pathways that cannot be easily predicted empirically.

Superhydrophobic polycarbosilane membranes for purification of solar hydrogen

Superhydrophobic membranes composed of an organic-inorganic hybrid polymer, namely polycarbosilane (PCS) with Mw of 4–8.9 × 103, were formed on a mesoporous γ-Al2O3-modified α-Al2O3 porous support. Under dry condition at 50 °C, the supported PCS membranes exhibited H2 permeance of 1.1–1.6 × 10−6 mol·m−2·s−1·Pa−1 and H2/N2 selectivity of 9.7–12.6 together with unique H2/He selectivity of 1.4–1.6. Even under saturated humidity at 50 °C, H2 permeance remained at 7.7 × 10−8 mol−1 m−2 s−1 Pa−1 with improved H2/N2 selectivity of 26. Moreover, when the measurements were performed using a H2-N2 (2:1) mixed feed gas as a simulated syngas produced by novel solar hydrogen production systems, the H2 permeance almost unchanged, while the N2 permeance was below the limit of detection. These results revealed a great potential of PCSs to develop novel H2-selective membranes for purifying solar hydrogen under high-humidity conditions around 50 °C. Further study on the gas permeation behaviors of He, H2 and N2 suggested that the enhanced H2/N2 selectivity under the high-humidity conditions could be explained by the synergistic effect of preferential H2 permeation through the dense PCS network governed by the solid state diffusion mechanism and blockage of N2 permeation through micropore channels within the PCS network by the permeate H2O-induced plugging at around the hetero interface between the superhydrophobic PCS and highly hydrophilic γ-Al2O3.

Corrosion mechanisms of ferritic-martensitic P91 steel and Inconel 600 nickel-based alloy in molten chlorides. Part II: NaCl-KCl-MgCl2 ternary system

Molten chlorides are promising heat transfer fluids (HTF) and thermal energy storage (TES) materials for third-generation concentrated solar power (CSP) plants. Despite their low cost and wide operating temperature ranges (400–800 °C), structural materials experience severe corrosion in commercially available chloride salts. The understanding of the corrosion mechanisms is therefore critical for successful plant design to ensure constant power generation over the 30 years of expected lifetime. This work investigates the corrosion behavior of ferritic-martensitic P91 steel and Inconel 600 nickel-based alloy in molten NaCl-KCl-MgCl2 (24.5-20.5-55.0 wt%) under isothermal conditions at 700 °C in Ar. For both alloys, the corrosion attack is associated with the selective dissolution of Cr and the removal of Cr-rich carbides from the alloy matrix leaving subsurface voids. The initial “impurity-driven” corrosion mechanism associated with the cathodic reduction of MgOH+ impurities leads to the formation of insoluble MgO on the substrates’ surface. Compositional and microstructural features of the alloys, especially the distribution of Cr-rich carbides as well as the solubility and mobility of carbon within the metallic matrix, are found to significantly affect their corrosion resistance. The experimental observations indicate, that the formation of galvanic pairs and solid-state diffusion mechanisms play a major role regarding the corrosion attack of the alloys. The systematic corrosion experiments conducted in this study indicate a lower corrosiveness of NaCl-KCl-MgCl2 ternary mixture than that of NaCl-KCl binary mixture in static conditions at 700 °C under Ar. This work gives significant insights into corrosion issues that may be expected in third-generation industrial CSP plants.

Intermetallic formation of Al-Fe and Al-Ni phases by ultrafast slurry aluminization (flash aluminizing)

Aluminizing of Fe and Ni-based substrates is a conventional process often made by gas phase related techniques (CVD, pack cementation and above the pack), whereby the coating thickness is controlled by solid-state diffusion. Similar coatings can be achieved by slurry aluminizing where self-propagating high temperature synthesis and solid-state diffusion mechanisms are involved. The present work investigates ultrafast (5 min annealing) aluminization to reduce coating time and compares the results on pure iron and nickel substrates with a conventional slurry aluminizing treatment (2 and 5 h). The use of fast heating ramps (25 and 100 °C/min) led to outwardly diffused coatings even with very high Al slurry activities. On nickel, the coatings were homogeneous while on iron, Kirkendall porosity occurred in the outermost layers due to the great dissolution of Fe in the Al melt and its subsequent outward diffusion towards to the Al source.

Investigation of Indium Oxide Nanowire Transform to Indium Zinc Oxide (IZO) Via Solid State Reactions

Transition metal oxide nanowires have attracted considerable attention due to their physical characteristics, chemical characteristics, and versatile applications. Among them, indium oxide (In203) nanowires demonstrate promising structure and electrical properties. Simultaneously, it used to be the reactants to synthesize indium zinc oxide (IZO) by solid-state reaction. The applicability would be highly related to the microstructure and synthesis process. Hence, study of conversion kinetics of IZO is essential. However, only few studies have mentioned the formation process of IZO and the solid-state diffusion mechanism. In this work, we successfully observed the transformation of novel IZO nanowire from interesting diffusion behavior between single-crystalline In2O3 nanowires and zinc oxide (ZnO). High resolution transmission electron microscope (HRTEM), fast Fourier transform (FFT) diffraction patterns and energy-dispersive spectrometer (EDS) were used for structural and compositional analysis. Based on the HRTEM images and the corresponding FFTs, the triclinic IZO was defined. Meanwhile, The in-situ TEM and EDS analysis provide the formation behavior and elemental distribution to elucidate the diffusion mechanism. This work exhibited the IZO nanowires with a unique structure and interesting formation behavior. Moreover, the study provides the improvement of controllability of conversion microstructure for further device applications. Figure 1

Investigation of Indium Oxide Nanowire Transform to Indium Zinc Oxide (IZO) Via Solid State Reactions

Transition metal oxide nanowires have attracted considerable attention due to their physical characteristics, chemical characteristics, and versatile applications. Among them, indium oxide (In203) nanowires demonstrate promising structure and electrical properties. Simultaneously, it used to be the reactants to synthesize indium zinc oxide (IZO) by solid-state reaction. The applicability would be highly related to the microstructure and synthesis process. Hence, study of conversion kinetics of IZO is essential. However, only few studies have mentioned the formation process of IZO and the solid-state diffusion mechanism. In this work, we successfully observed the transformation of novel IZO nanowire from interesting diffusion behavior between single-crystalline In2O3 nanowires and zinc oxide (ZnO). High resolution transmission electron microscope (HRTEM), fast Fourier transform (FFT) diffraction patterns and energy-dispersive spectrometer (EDS) were used for structural and compositional analysis. Based on the HRTEM images and the corresponding FFTs, the triclinic IZO was defined. Meanwhile, the in-situ TEM and EDS analysis provide the formation behavior and elemental distribution to elucidate the diffusion mechanism. This work exhibited the IZO nanowires with a unique structure and interesting formation behavior. Moreover, the study provides the improvement of controllability of conversion microstructure for further device applications.

Sintering effects on additive manufactured Ni–Mn–Ga shape memory alloys: a microstructure and thermal analysis

This work investigates the effects of time dependency for isothermal sintering on additive manufactured Ni–Mn–Ga magnetic shape memory alloys. Binder jetting additive manufacturing was used to produce Ni–Mn–Ga parts from pre-alloyed powders. Additive manufacturing via the binder jetting technique produces parts with intrinsic porosities, based on the morphology of the source material. The Ni–Mn–Ga parts printed in this study using the binder jetting method possessed average densities of ~ 46% before sintering. These samples were sintered at 1353 K in increments of 10 h up to 50 h. Based on this temperature and time frame, (1) microstructural evolution, (2) crystallographic phase analysis, (3) transformation behaviors, and (4) thermal–physical properties were investigated. The additive manufactured Ni–Mn–Ga samples exhibited increases in densities, from ~ 74 to ~ 83% due to solid-state diffusion mechanisms. X-ray diffraction reveals that all of the additive manufactured samples have the 5 M martensitic phase at room temperature. Reversible martensitic transformation temperatures were recorded during heating and cooling cycles through differential scanning calorimetry, which indicate austenitic phase transformations occurring slightly above ambient temperatures. Additionally, analysis of the heating and cooling cycles prescribes that the entropy and Gibb’s energies decrease over the reversible martensitic transformations as sintering time increases. It is envisioned that this study will support a more synergistic manufacturing process between binder jetting additive manufacturing and post-heat treatment processes for Ni–Mn–Ga shape memory alloys.

Synthesis and characterization of a silica-alumina composite membrane and its application in a membrane reactor

Abstract Hydrothermally stable silica-alumina composite membranes were synthesized through chemical vapor deposition (CVD) of tetraethylorthosilicate (TEOS) and aluminium tri-sec-butoxide precursor at 923 K on porous alumina supports. The membranes showed high hydrogen permselectivity (order of 10−7 mol m−2 s−1 Pa−1) comparable to that of pure silica membranes but with superior hydrothermal stability, and were used in a membrane reactor. The permeation of small gas species (H2, He, Ne) was well explained by a solid-state diffusion mechanism, involving jumps of the permeating species between solubility sites. The permeation mechanism of large gas molecules (CH4, CO2, N2) was explained by the gas translation mechanism involving large pore defects. Steam methane reforming (SMR) on a Ni/MgO-SiO2 catalyst was carried out at 923 K in the membrane reactor and in a conventional packed-bed reactor. The membrane contributed to an increase in the hydrogen production rate by the selective extraction of hydrogen from the reaction zone.

Microstructural and Diffusion Analysis of Au-Sn Diffusion Couple Layer Undergoing Heat Treatment at Near Eutectic Temperatures

Diffusion couples of pure gold and pure tin were created by mechanical cold rolling method. The couples were isothermally treated at temperatures slightly above and below the eutectic temperature near tin-rich region of the equilibrium phase diagram. Differences in the diffusion behaviors were observed as a function of treatment temperatures below (473 K) and above (498 K) the eutectic temperature. At the boundary, it was found that first solid state inter-diffusion was initiated which resulted in local compositional change and solid-state formation of intermetallic compounds. As the composition shifts away towards mixing, the growth of the intermetallic phases was monitored as a function of temperature and time. At temperature above the eutectic, there may be a liquid fraction as the interface isothermally melted. The kinetic involves dissolution of Au atoms into locallized tin-rich liquid. At below eutectic temperature, the formation and growth kinetic of phases follows a solid state diffusion mechanism. By investigation the exponent n values in the growth equation l=k(t/t0)n, the values were found to be in between 0.62 - 0.77 which implies that the kinetics of IMC formations experiment are controlled by both diffusion and intermetallic reaction. The bonding temperature was found to be faster and more reliable at bonding temperature slightly above the eutectic.

Investigation of Solid State Diffusion Processes Involved in the Zinc Oxide Sulfidation Reaction

Sulfidation of undoped and aluminum doped zinc oxide materials has been performed by TGA under a H2S atmosphere in order to evaluate the impact of the doping element on sulfidation reaction kinetics and mechanism. The presence of aluminum seems to slow-down the reaction kinetics. This phenomenon might be explained by a modification of the solid state diffusion processes involved in ZnO sulfidation reaction and the related ZnS outward growth, assuming the presence of aluminum atoms inside ZnO and ZnS phases. In order to determine solid state diffusion mechanisms controlling the reaction kinetics, molecular dynamics simulations were performed using a Coulomb-Buckingham potential. Firstly, the diffusion of the different elements (Zn, O, S) was simulated for both the oxide and sulfide phases considering a vacancy mechanism. Secondly, simulations of the oxide phase doped by a trivalent cation were also performed. The results obtained in this preliminary work are presented and compared to the literature.

Solid-flame: Experimental validation

The tantalum–carbon reactive system possesses a high energy of reaction with an adiabatic combustion temperature of 2743 K, which is significantly below the melting points of the reactants, as well as any intermediate phases and final products. It was suggested that a combustion wave could propagate in Ta+C mixtures solely owing to a solid–solid reaction. However, this combustion process has never been shown to occur without gas-assisted transport. Here, we report preparation of highly pure and pore-free Ta/C composite particles, which were used for experimental validation of the solid-flame. Preparation of these composite particles involves short term high-energy ball milling (HEBM) of tantalum and carbon powders. High-resolution microscopy coupled with three-dimensional reconstruction techniques were used to characterize the volume nanostructure of mechanically fabricated composite particles. It was quantitatively shown that the particles have nano-scale mixing of the reagents and possess high contact surface area between tantalum and carbon. Experiments revealed that the ignition temperature of as fabricated composite particles is 1243 ± 15 K and maximum combustion temperature was shown to be 2487 ± 50 K, which is well below any possible solid–liquid transitions. Utilizing results obtained with composite particles prepared under different HEBM conditions, it is shown that carbon diffusion through the tantalum grain boundaries and subsequent formation of a Ta(C) solid solution defines low temperature ignition of mechanically fabricated particles. The high surface area contact between the Ta and C nano-scale reagents allows the reaction to propagate in a self-sustained manner, owing solely to a solid-state diffusion mechanism.

ChemInform Abstract: Selectivities in Post‐Synthetic Modification of Borosilicate Zeolites

AbstractReview: 173 refs.

Selectivities in Post-Synthetic Modification of Borosilicate Zeolites

The chemistry of post-synthetic modification of borosilicate zeolites, and their understanding and use in catalytic applications are reviewed. First, a survey is given on the practical application of solid state NMR to follow the structural properties of boron. Then, the hydrolytic chemistry of boron in zeolites is summarized with a focus on selective reactivities of trigonal boron created by counterions, and stepwise extraction of boron from the framework. The reinsertion of other heteroatoms (mainly Al is discussed here) can be carried out by three different methods with different selectivities. First, the extent of Al reinsertion can be tailored quantitatively by controlling boron removal and vacancy formation with appropriate counterions. Secondly, the substitution of Al for B can be kinetically retarded by using uncalcined as-made zeolites with organic structure directing agents still occluded in the pores. Although these zeolites are not porous, quantitative replacement of framework atoms (Al for B) is possible, most likely by a solid state diffusion mechanism. Finally, Al reinsertion can be efficiently achieved in aqueous Al(NO3)3 solution under acidic conditions and is pore selective. This is due to the finding that the hydrated aluminum cations are too bulky for medium-sized pores, so that preferably 12-membered ring pores can be aluminated, and 10-membered ring pores do not substitute Al for B. This substitution can be quantitatively followed by the pH change in the zeolite/Al(NO3)3 slurry. A variety of catalytic test reactions are used to characterize the catalytic properties of the aluminosilicate zeolites prepared via post-synthetic treatment of their borosilicate counterparts.

Influence of the heating rate on the in situ synthesis and consolidation of ZrB2 by reactive Spark Plasma Sintering

The effect of the heating rate during reactive SPS to obtain dense ZrB2 from elemental reactants is investigated. When the temperature is increased at 500 °C/min or faster, the synthesis reaction evolves under combustion regime. In contrast, if heating rates equal or lower than 200 °C/min are considered, a gradual solid-state diffusion mechanism is established. In both cases, the synthesis reaction goes to completion during the non-isothermal heating step, although samples have to be processed for 20 min at 1850–2000 °C and 50 MPa to reduce residual porosity. Despite of the combustion synthesis route allows to obtain pure dense products at milder temperature conditions, safety problems and product inhomogeneity make its exploitation not convenient. On the other hand, safety conditions are preserved during the gradual formation of ZrB2 by SPS. Correspondingly, 96% dense monolithic products can be obtained at temperature levels of about 2000 °C within 20 min dwell time.

Improved kinetic model for water splitting thermochemical cycles using Nickel Ferrite

In a previous work of the authors (AIChE Journal 2013; 59(4): 1213-1225) on the characterization of the performance of redox material compositions during two-step thermochemical splitting of water, it was observed that fitting of the obtained hydrogen and oxygen concentration profiles with a reaction model based on simple first order reaction rates could describe adequately only the first part of the evolution curves. This suggested that more complicated reaction models taking into account the structure of the redox material are needed to describe the whole extent of the experimental data. Based on the above, a minimum set of experiments for water splitting thermochemical cycles over a Nickel-ferrite was deigned and performed involving an increased duration of the reaction steps. A new extended model was derived for the water splitting and thermal reduction reactions, which considers two oxygen storage regions of the redox material communicating to each other by a solid state diffusion mechanism. The inclusion of two state variables instead of one has a significant effect on the reaction dynamics and renders the model capable to explain the dynamics of the convergence of the thermochemical cycles to a periodic steady state, observed experimentally in the previous work.

Utilization of Coke Oven Gas and Converter Gas in the Direct Reduction of Lump Iron Ore

The application of off-gases from the integrated steel plant for the direct reduction of lump iron ore could decrease not only the total production cost but also the energy consumption and CO2 emissions. The current study investigates the efficiency of reformed coke oven gas (RCOG), original coke oven gas (OCOG), and coke oven gas/basic oxygen furnace gas mixtures (RCOG/BOFG and OCOG/BOFG) in the direct reduction of lump iron ore. The results were compared to that of reformed natural gas (RNG), which is already applied in the commercial direct reduction processes. The reduction of lump ore was carried out at temperatures in the range of 1073 K to 1323 K (800 °C to 1050 °C) to simulate the reduction zone in direct reduction processes. Reflected light microscopy, scanning electron microscopy, and X-ray diffraction analysis were used to characterize the microstructure and the developed phases in the original and reduced lump iron ore. The rate-controlling mechanism of the reduced lump ore was predicted from the calculation of apparent activation energy and the examination of microstructure. At 1073 K to 1323 K (800 °C to 1050 °C), the reduction rate of lump ore was the highest in RCOG followed by OCOG. The reduction rate was found to decrease in the order RCOG > OCOG > RNG > OCOG-BOF > RCOG-BOFG at temperatures 1173 K to 1323 K (900 °C to 1050 °C). The developed fayalite (Fe2SiO4), which resulted from the reaction between wustite and silica, had a significant effect on the reduction process. The reduction rate was increased as H2 content in the applied gas mixtures increased. The rate-determining step was mainly interfacial chemical reaction with limitation by gaseous diffusion at both initial (20 pct reduction) and moderate (60 pct reduction) stages of reduction. The solid-state diffusion mechanism affected the reduction rate only at moderate stages of reduction.

Solid state diffusion between Sn and Cu microcones on Cu microcones

Abstract Theoretical study of solid state diffusion mechanism in low-temperature bonding method based on Cu microcones is reported. A Sn layer was electrodeposited on Cu microcones as well as flat Cu substrate then annealed at bonding temperature 463 K. IMC grains of Sn/Cu-microcones diffusion samples grew with a relatively fine and uniform size. Cu 6 Sn 5 crystal orientation in Sn/Cu-microcones and Sn/flat-Cu diffusion samples were different according to X-ray diffusion patterns. Nucleation was more likely to occur near the pinpoints of the Cu microcones. The kinetic factors showed that the special morphology of Cu microcones was beneficial for the growth of intermetallic layer (Cu 6 Sn 5 ) in short annealing time and the grain boundary diffusion partially contributes to the rate-controlling process.

Fe2(MoO4)3/MoO3 nano-structured catalysts for the oxidation of methanol to formaldehyde

Nano-structured iron molybdate materials, comprising Fe2(MoO4)3 nano-particles anchored onto MoO3 nano-rods, have been synthesised and evaluated as catalysts for the selective oxidation of methanol to formaldehyde. The catalysts were benchmarked against a standard iron molybdate catalyst prepared by co-precipitation and were found to have comparable performance under the test reaction conditions. The materials have been characterised using a combination of electron microscopy, powder X-ray diffraction and Raman spectroscopy. The synthesised MoO3 nano-rods were found to have a uniform structure, 8–10μm in length with a rectangular cross-section of 50–100nm×100–200nm. Fe was impregnated onto the MoO3 nano-rods via incipient wetness with an aqueous solution of Fe(NO3)3·9H2O. Calcination of these precursors formed 20–200nm Fe2(MoO4)3 islands on the surface of the nano-rods via a solid-state diffusion mechanism, and the size of the Fe2(MoO4)3 islands could be controlled by varying the Fe loading. The effect of the temperature and duration of calcination were investigated, and it was found that the optimum conditions were 450–500°C for 2h. At 350°C, the temperature was too low for the solid-state reaction between the MoO3 nano-rod and the surface Fe to occur, and no Fe2(MoO4)3 was formed. At higher temperatures, the nano-rod morphology was compromised, and irregular, partially coalesced particles of Fe2(MoO4)3 were generated, which had a lower catalytic performance than the nano-structured Fe2(MoO4)3/MoO3 materials. At 400°C, the solid-state reaction occurred sufficiently slowly for mechanistic aspects of the Fe2(MoO4)3 island formation to be elucidated by transmission electron microscopy.

Generation of silver-anatase nanocomposite by excimer laser-assisted processing

We demonstrate crystallization of the anatase thin film with self-adhering silver nanoparticles (Ag NPs) by a single-step laser process. Titanium dioxide (TiO2) sol-gel precursor film was deposited on glass substrate and Ag ions were adsorbed from silver nitrate aqueous solution. A nanosecond (ns) pulsed beam of KrF (248 nm) laser was traversed across the amorphous Ag-TiO2 film leading to crystallization of the anatase and simultaneous generation of cubic as well as hexagonal Ag NPs. A uniform size distribution of Ag NPs was observed with an average size of 9.6 nm. On the other hand, anatase grains were 38 nm in size as determined by X-ray diffraction (XRD) and scanning transmission electron microscope (STEM). Analytical simulations indicated a solid-state diffusion and phase transformation mechanism dominating within the film due to laser treatment.