Diffusion Annealing Research Articles

In situ investigation of the fracture of primary carbides and its mechanism in M50 steel

The tensile crack initiation and propagation of M50 bearing steel were investigated. It is found that the primary carbides were fractured during the tensile test by in situ SEM, while decohesion of the carbide/matrix interface was hardly observed. In order to capture the initial tensile crack, quasi-in situ X-ray microtomography was performed, indicating that the earliest crack was formed from the broken interior carbides. This indicates that multiple cracks already existed in the matrix when they were observed on the sample surface. Electron backscattered diffraction (EBSD) and the finite element method (FEM) were applied to analyze the fracture behavior of carbide particles. The fracture of carbide particle is produced by the incompatible deformation between the matrix and carbides. The frequency of carbide fracture was found to be related with its fracture strength, size and shape. M 2 C carbide fracture was more easily broken than the MC carbide during tensile test. In addition, the long axis of most M 2 C carbides is approximately parallel to its (0001) plane and normal to tensile stress, leading to cracking more easily. Finally, a suggestion of adding pre-deformation is proposed to make M 2 C carbides broken sufficiently and further refine the primary carbides. • X-ray microtomography is applied to analyze the evolution of primary carbides. • Incompatible deformation between the matrix and particles leads to carbide fracture. • M 2 C carbide is more easily broken than MC carbide. • Pre-deformation before diffusion annealing should be applied to refine carbides.

Influence of heat treatment on tribocorrosion properties of Ni-B composite coatings

Various surface protection technologies, in particular, electrochemical, are used to increase the wear and corrosion resistance of steels and alloys. Composite electrochemical coatings (CEC) technology is more promising than "pure" galvanic coatings. Application of CEC increases the wear, corrosion and fatigue failure resistance of metals. Nickel often is chosen as a CEC matrix because it easily forms uniformly filled defect-free composite structures with many particles of the dispersed phase (DP).
 Physical and mechanical properties of metal coatings determine practical application of such composition. The characteristics of nickel-based CEC are: high hardness and strength, significant corrosion resistance in atmospheric environment, as well as in alkali and mild acidy environments. An effective composition coating with tribological designation can be CEC Ni-B, received in the process of electrolysis from suspension of amorphous boron in nickel electrolyte. A new composite structure of matrix filled type Ni-Ni3B is formed after heat treatment. Composition and structure of coating is determined by regimes of diffusion annealing. Ni-B coatings increase wear resistance of steel in chlorine-based environments. The influence of low-temperature thermal treatment of Ni-B CEC on steel 09Mn2Si on their tribocorrosion behavior is investigated. It is shown that the structural factor has a decisive influence on the efficiency of such friction pairs. The CEC has the least wear and the most positive compromise electrode potential after vacuum annealing at 450°C, when the initial stage of solid-phase interaction of coating components with the formation of Ni-Ni3B occurs.

Diffusion from a constant source along nonequilibrium dislocation pipes

We propose new theoretical description of diffusion features along nonequilibrium dislocation pipes. The excess energy of nonequilibrium dislocation pipes is introduced. The effective diffusion coefficient in nonequilibrium dislocation is calculated and analyzed taking into account the relaxation processes during diffusion annealing. The equation of nonequilibrium diffusion from a constant source in dislocation pipes is derived. The analytical solution of formulated equation describing the diffusant concentration in dislocation pipe is found. The diffusant concentration and the amount of diffusant at a fixed depth increase with an increase in nonequilibrium dislocation excess energy. We observe the maximum of time dependence of diffusant concentration caused by an increase in nonequilibrium dislocation excess energy and relaxation processes during diffusion annealing.

Diffusion in polymer-derived Si–(B–)C–N ceramics, particularly amorphous Si29B9C41N21

Abstract The diffusion coefficients (D) of implanted radioisotopes – 71Ge, 31Si, and 11C – in the polymer-derived amorphous (a-)Si29B9C41N21 ceramic have been measured as functions of temperature (T) in different as-pyrolysed states (71Ge) or after pre-diffusion annealing at 1600 °C for 2 h (71Ge, 31Si, and 11C) by means of radiotracer techniques, in which serial sectioning was done by ion-beam sputtering. In the cases of 31Si (half-life t 1/2 = 2.6 h) and 11C (t 1/2 = 20.4 min), implantation, diffusion annealing, and sputter-sectioning were done on beamline and in situ of a novel set-up specially constructed for diffusion studies of short-lived radiotracer atoms. In all cases, the T-dependencies of D are of Arrhenius type. Comparing the Arrhenius parameters of D(71Ge) to previous data on diffusion in (B-free) a-Si28C36N36, it is concluded that the diffusion of 71Ge in the a-Si29B9C41N21 ceramic is controlled by vacancies in its a-Si3N4 –y C y phase which become increasingly smeared out when the C-content y decreases as a result of pre-annealing. The coincidence of D(31Si) and D(11C) in pre-annealed a-Si29B9C41N21 at all temperatures investigated is enforced by vacancy-mediated diffusion through SiC crystallites embedded in the a-Si3N4 –y C y phase.

Effect of diffusion annealing on duplex coated pure titanium produced by hot-dip aluminizing and micro-arc oxidation

In the present study, an Al2O3 ceramic coating was formed on a pure titanium surface with the application of the duplex coating technology produced by combining hot-dip aluminizing (HDA) and micro-arc oxidation (MAO) processes. Due to the porous nature of MAO coating with the structural and mechanical differences between the MAO (Al2O3) and HDA layers (Al, Al3Ti), diffusion annealing treatment was applied to duplex coated (HDA + MAO) titanium samples. With the diffusion annealing treatment, a composite layer with a thickness of about 125 μm was formed beneath the modified MAO coating, which showed a denser structure by penetrating TiO2 into the MAO. MAO coatings with and without diffusion annealing exhibited compressive residual stresses with values of −1530 and −850 MPa, respectively. Microhardness and elastic modulus of the diffusion annealing-treated MAO coating reached 1230.1 HV and 241.3 GPa, respectively. The diffusion annealing-treated MAO coating provided ~29% less coefficient of friction and ~8.4 times greater relative wear resistance than that of MAO coating without diffusion annealing.

Scratch resistance of cobalt boride layer subjected to a diffusion annealing process

This work studies the effect of a diffusion annealing process in cobalt boride layers by progressive load scratch (PLST) and multipass scratch (MPST) tests. First, a double-phase CoB/Co2B layer was formed on CoCrMo alloy at 1000 °C for 6 h. Next, a single-phase Co2B layer was obtained through a diffusion annealing process. The scratch tests were conducted with a progressive load from 5 to 150 N in PLST, whereas in MPST, up to 400 passes were applied with a subcritical load of 38 N. Conducting the diffusion annealing process significantly improved the scratch resistance; in PLST, the achieved layer avoided severe failure mechanisms and decreased residual depth by 60%. In MPST, friction was reduced and the volume loss decreased around 50%.

Zircon (U-Th)/He thermochronology of Grand Canyon resolves 1250 Ma unroofing at the Great Unconformity and <20 Ma canyon carving

Abstract Our study used zircon (U-Th)/He (ZHe) thermochronology to resolve cooling events of Precambrian basement below the Great Unconformity surface in the eastern Grand Canyon, United States. We combined new ZHe data with previous thermochronometric results to model the <250 °C thermal history of Precambrian basement over the past >1 Ga. Inverse models of ZHe date-effective uranium (eU) concentration, a relative measure of radiation damage that influences closure temperature, utilize He diffusion and damage annealing and suggest that the main phase of Precambrian cooling to <200 °C was between 1300 and 1250 Ma. This result agrees with mica and potassium feldspar 40Ar/39Ar thermochronology showing rapid post–1400 Ma cooling, and both are consistent with the 1255 Ma depositional age for the Unkar Group. At the young end of the timescale, our data and models are also highly sensitive to late-stage reheating due to burial beneath ∼3–4 km of Phanerozoic strata prior to ca. 60 Ma; models that best match observed date-eU trends show maximum temperatures of 140–160 °C, in agreement with apatite (U-Th)/He and fission-track data. Inverse models also support multi-stage Cenozoic cooling, with post–20 Ma cooling from ∼80 to 20 °C reflecting partial carving of the eastern Grand Canyon, and late rapid cooling indicated by 3–7 Ma ZHe dates over a wide range of high eU. Our ZHe data resolve major basement exhumation below the Great Unconformity during the Mesoproterozoic (1300–1250 Ma), and “young” (20–0 Ma) carving of Grand Canyon, but show little sensitivity to Neoproterozoic and Cambrian basement unroofing components of the composite Great Unconformity.

Evolution of the Structure and Grain Boundary Ensemble of Nickel during Diffusion Annealing under Conditions a Segregating Impurity (Silver) on Grain Boundaries

Evolution of the Structure and Grain Boundary Ensemble of Nickel during Diffusion Annealing under Conditions a Segregating Impurity (Silver) on Grain Boundaries

Production of low-scandium Al – Mg alloys

The work was performed at the laboratory plant of semi-continuous casting of ingots (LPSCC) of the Institute of non-ferrous metals and materials science of SFU in order to obtain deformed semi-finished products with specified performance characteristics. The paper presents the results of obtaining an Al – Mg alloy doped with zirconium and scandium. Experimental rolling ingots were cast using casting modes that provide the structure parameters of the cast billet as close as possible to the parameters obtained in industrial conditions for ingots with a thickness of at least 300 mm. This paper presents the modes of two-stage diffusion annealing. The modes of hot and cold rolling of the experimental alloys obtained at the laboratory plant of semi-continuous casting of ingots are given. he paper presents the microstructure of the studied alloys in the cast and annealed state. The paper presents the results of research on the strength and plastic characteristics of deformed semi-finished products from experimental ingots of Al – Mg alloy with a scandium content of less than 0.1 %. The article presents comparative studies of six experimental alloys with an average content of the variable element Sc from 0.054% to 0.075%, respectively. The article shows that when the average concentration of Sc decreases to 0.054%, it is not possible to achieve the specified level of mechanical properties, due to the insufficient total concentration of the alloying element (Sc) in experimental alloys, which provides the effect of quench age hardening during the decomposition of solid solutions of scandium with the formation of intermetallic Al3Sc. It was shown that it is possible to reduce the concentration of scandium in the composition of Al–Mg alloys to 0.075% with the achievement of high performance characteristics: not lower than tensile strength — 390 MPa, proof strength — 275MPa, percentage of elongation — 12 %. The research was carried out within the framework of the State assignment by the laboratory of low-carbon metallurgy and power engineering of Siberian Federal University, as a participant company of REC «Yenisei Siberia» within the national project “Science and universities”.

Search for copper diffusion at hybrid bonding interface through chemical and electrical characterizations

Cu/SiO2 diffusion at hybrid bonding interface without diffusion barrier was investigated in order to validate the electrical insulation of interconnects. The Cu thermal diffusion was studied by ToF-SIMS analysis of the dielectrics stack facing bonding pads after a bonding annealing (400 °C, 2 h) and a diffusion annealing (400 °C, 14 h). No trace of copper was found above the limit of detection 1017 at·cm−3. Cu ions drift was followed by I-V measurements on specially designed comb-serpentine that maximize the electrical field at bonding interface. Their efficiency was confirmed since physical failure analysis located the dielectric breakdown damage between bonding pads. Breakdown voltages coupled to wafer-to-wafer misalignments enabled the extraction of the SiO2 breakdown strength: 3.4 MV·cm−1. This study proves that at room temperature, hybrid bonding interconnects remain electrically insulated despite thermal budgets involved by the bonding process.

High thermoelectric power factors in polycrystalline germanium thin films

The high potential of polycrystalline Ge as a thin-film thermoelectric material was demonstrated. We synthesize a polycrystalline Ge layer on an insulating substrate at 450 °C via advanced solid-phase crystallization and control its carrier concentration through the solid-phase diffusion of various p- and n-type dopants. The heating deposition (150 °C) of the amorphous precursor considerably improves the crystal quality of the polycrystalline Ge layer as well as the doping properties. The solid-phase diffusion of Ga and P dopants onto the Ge layers allows for control of the carrier concentration in the ranges of 1017–1020 cm−3 for p-type and 1018–1019 cm−3 for n-type, respectively, by modulating the diffusion annealing temperature and time. Because of the high electrical conductivities reflecting the carrier mobilities and carrier concentrations, the maximum power factors reach a value of 1080 μW m−1 K−2 for p-type and 2300 μW m−1 K−2 for n-type at room temperature. These power factors are higher than those of most polycrystalline semiconductor thin films formed at temperatures below 1000 °C. Therefore, this study serves as a milestone toward high-performance and reliable thin-film thermoelectric generators based on an environmentally friendly semiconductor.

Contact Surfaces Preparation in Manufacturing of Bimetallic Strips CuZn10 Brass - C22E Steel - CuZn10 Brass

Contact surfaces preparation before cold cladding is one of the most important technological operations. A joint plastic components deformation of the of bimetal 1 according to OST 3-6648-91 and bimetal 3 according to OST 3-6649-91 CuZn10 brass - C22E steel - CuZn10 brass (according to EN standard) should be performed with the strongest possible compression to obtain the required layers connection strength, ensuring strip winding into a roll without delamination. We investigated influence of some factors on the bond strength of bimetal layers: surface hardening of contact surfaces, presence of an underlayer on a steel base, contact surfaces micro geometry, components heating temperature in the deformation zone, diffusion annealing after cladding and a bimetal layers thicknesses ratio effect. Cold cladding technological recommendations have been developed for manufacturing of bimetal 1 according to OST 3-6648-91 and bimetal 3 according to OST 3-6649-91 (CuZn10 brass - C22E steel - CuZn10 brass).

The diffusion path in Ti-Ni70Cu30 diffusion couple at 850 °C for different annealing times

The interdiffusion in Ti-Ni70Cu30 diffusion couple was studied at 850 °C at times varied between 10 and 300 min. The diffusion paths for the samples were determined and the order of intermetallic phases occurring in the diffusion zone was established. It was concluded that after 10 and 30 min of diffusion annealing, four intermetallic phases formed, namely: Ti2Ni, TiNi, τ1 and TiNi3. Between 30 and 60 min, also the Ti2Cu phase appeared next to Ti2Ni phase forming the multi-zone region, which thickness almost doubled between 60 and 300 min of diffusion annealing at 850 °C. The formation of Ti2Cu and the multi-zone region was explained by the enrichment of Cu at the Ti2Ni/Ti boundary and connected with the increase in its diffusion flux.

СТРУКТУРООБРАЗОВАНИЕ ПРИМЕСНЫХ ПРЕЦИПИТАТОВ НИКЕЛЯ В КРЕМНИИ

In this study, using the method of electron probe analysis, the sequence of formation of various impurity precipitates of nickel in silicon in the process of diffusion doping at a temperature of T = 1573 K was investigated. The influence of the value of the cooling rate of the samples after diffusion annealing on the formation of impurity precipitates was considered. The morphological parameters of impurity precipitates of nickel in silicon have been revealed, and their chemical compositions have been determined. It was found that, depending on the size and shape, the nickel precipitates can have a single or multilayer structure

Influence of the diffusion annealing process in the corrosion susceptibility of cobalt boride layer immersed in Hank's solution

The corrosion susceptibility of borided CoCrMo alloy exposed to a diffusion annealing process (DAP) and immersed during 7 days in a Hank's solution was evaluated, being compared with the results obtained in the borided CoCrMo alloy and the CoCrMo alloy. Firstly, the CoCrMo alloy was exposed to the powder-pack boriding process during 5 h at 1273 K, to obtain a biphasic layer (CoB-Co2B) with a total thickness around 33 μm. Then, the DAP was performed on the borided CoCrMo alloy during 2 h at 1273 K in an inert argon atmosphere to obtain a 29 μm of monophasic Co2B layer. The corrosion tests were performed by the potentiodynamic polarization technique to estimate the corrosion resistance (Rp) and the corrosion current density (jcorr) by means of the linear polarization and the Tafel extrapolation techniques, respectively. The results showed, in the 7th day of immersion in the Hank's solution, that the borided CoCrMo alloy exposed to the DAP exhibited a corrosion value ~22 times higher (~357 kΩ cm2) than that obtained in the borided CoCrMo alloy (~15 kΩ cm2), reaching a value close to the CoCrMo alloy (~385 kΩ cm2). The corrosion performance of the borided CoCrMo alloy exposed to the diffusion annealing process was attributed to i) the presence of the monophasic Co2B layer and high contents of Cr and Mo on the outer-zone of the borided surface, and ii) the depletion of the B2S3 and CrPO4 species at the surface of the borided CoCrMo alloy. Finally, the borided CoCrMo alloy exposed to the DAP exhibited a corrosion susceptibility around 7%, meanwhile the borided CoCrMo alloy obtained a value of 96%, approximately.

Study on the Fine Grain Size and Microhardness at the Interface of AZ31/Mg‐Y Composites

AZ31/Mg‐Y/AZ31 composites are fabricated by hot rolling bonding. To identify the formation mechanism of the microstructure in the interface adjacent region, additional hot rolling or/and diffusion annealing are also conducted on the base of the initial AZ31/Mg‐Y/AZ31 composite. Scanning electron microscopy, energy dispersive spectroscopy, and electron backscatter diffraction are used to characterize the microstructures and chemical compositional distributions. Vicker's microhardness tests are conducted to determine the local mechanical property. It is found that in the Mg–Y layer of the AZ31/Mg‐Y/AZ31 composite, the grain size in the interface‐adjacent region is much finer than that in the central part. Much finer Al2Y particles compared with those in the traditional Mg–Al–Y alloys are formed in the interface‐adjacent region. The formation of the fine grain in the interface‐adjacent region may be mainly related to the Al2Y particles rather than the accommodation deformation between layers. Both the grain refinement and the formation of Al2Y particles contribute to strengthening of the Mg–Y layer. The results in this work may provide a novel method to prepare fine and dispersed high‐melting‐point particles in Mg alloys, thus leading to strong and high‐thermal‐stability Mg alloys.

Temperature-dependent reversed fracture behavior of multilayered TiBw/Ti–Ti(Al) composites

Engineering strong and ductile structural materials has been an enduring pursuit over the past few decades. Here we proposed a heterogeneous laminated/gradient integrated strategy with the purpose of maximizing the role of laminated or gradient structure for performance enhancement. Such a heterogeneous TiBw/Ti–Ti(Al) composite is structurally characterized by a layered distribution of TiB whisker and a compositional gradient with depth, and fabricated by a simple diffusion annealing of alternately stacked TiBw/Ti and Al foils. The mechanical properties were evaluated at room and high temperatures, and the mechanism behind superior strength-ductility synergy was analyzed by post-mortem characterization of deformation physics and quantitative crack statistics. Our results demonstrated that the major stress-bearing constituents gradually changes from Ti(Al) to TiBw/Ti layers as the deformation temperature increases, leading to the temperature-dependent reversed fracture behavior. The contribution of sub-critical cracks is in particular discussed, and the key viewpoint we proposed is that the larger the crack density, the wider the crack distribution, the better the mechanical performance, as long as the sub-critical crack is still in its “stable” domain and does not develop into unstably critical major crack causing catastrophic fracture.

Photolithographically-patterned C-MEMS graphene by carbon diffusion through nickel

In recent years the most studied carbon allotrope has been graphene, due to the outstanding properties that this two-dimensional material exhibits; however, it turns out to be a difficult material to produce, pattern, and transfer to a device substrate without contamination. Carbon microelectromechanical systems are a versatile technology used to create nano/micro carbon devices by pyrolyzing a patterned photoresist, making them highly attractive for industrial applications. Furthermore, recent works have reported that pyrolytic carbon material can be graphitized by the diffusion of carbon atoms through a transition metal layer. In this work we take advantage of the latter two methods in order to produce multilayer graphene by improving the molecular ordering of photolithographically-defined pyrolytic carbon microstructures, through the diffusion (annealing) of carbon atoms through nickel, and also to eliminate any further transfer process to a device substrate. The allotropic nature of the final carbon microstructures was inspected by Raman spectroscopy (Average I D/I G of 0.2348 ± 0.0314) and TEM clearly shows well-aligned lattice planes of 3.34 Å fringe separation. These results were compared to measurements made on pyrolytic carbon (Average I D/I G of 0.9848 ± 0.0235) to confirm that our method is capable of producing a patterned multilayer graphene material directly on a silicon substrate.

Influence of natural oxide layers at Ni/NiAl interfaces on Ni3Al phase formation

The influence of natural oxide layers at interfaces in diffusion couples is studied. Concentration distributions at (Ni)/NiAl interfaces and the formation of the Ni3Al phase at 650 °C are characterized using scanning electron microscopy (SEM) and aberration corrected scanning transmission electron microscopy (STEM) with Energy-Dispersive X-ray spectroscopy (EDX) with unprecedented spatial resolution. Employing the common practice of chemical etching with 10 vol% HCl does not remove the oxide layers irrevocably – they are detected at the Kirkendall plane after diffusion annealing of (Ni)/NiAl diffusion couples, if high resolution microscopy is employed. The oxide layer at the Kirkendall plane is of a thickness of ~5 nm, comparable to that of the combined natural oxide layers on the (Ni) and NiAl surfaces. The oxide acts as a diffusion barrier, retarding or locally suppressing growth of Ni3Al into the (Ni) phase. For comparison, oxide-free Kirkendall planes were obtained by subjecting the joining surfaces of (Ni) and NiAl to gentle grinding with low contact pressure in a glove-box in purified Ar atmosphere before assembling the diffusion couple. After diffusion annealing, the Ni3Al layers are distinctly thicker and of a more homogeneous layer thickness as compared to samples with residual oxides. It is shown that evaluating interdiffusion coefficients in oxide-free diffusion couples yields higher values as compared to the conventionally assembled counterparts.

The reaction mechanism in the hydrothermal synthesis of Nd2Fe14B magnetic particles

Nd2Fe14B-based magnetic powders are essential in many applications. In this work, Nd2Fe14B hard magnetic particles were synthesised via hydrothermal techniques following a reduction–diffusion annealing process. The mechanism of Nd2Fe14B-particles formation was investigated via differential-scanning calorimetry and X-ray-diffraction; the results showed that Nd–Fe–B precursors of well-dispersed nanometre size were successfully synthesised via a hydrothermal reaction. The Nd–Fe–B oxides were composed of Fe2O3, NdFeO3 and NdBO3 (annealing at 900 ​°C) or amorphous BmOn (annealing at 700 and 800 ​°C). Reduction–diffusion (R–D) was a four-step process: first, the reduction of Fe2O3 to Fe occurred at 328 ​°C; second, NdBO3 was reduced to B and NdH2 at 341 ​°C; third, NdH2 and Fe were formed from NdFeO3 at 635 ​°C; and finally, the Nd2Fe14B phase was formed from NdH2, Fe and B at 659 ​°C. After removing the main by-product CaO, the coercivity of the as-synthesised Nd2Fe14B-based powder was 2.0 ​kOe. Analysis of the temperature-dependent magnetic properties revealed that coercivity was controlled by nucleation of the reversed magnetic domains.