Coherent Fcc Research Articles

Effect of combined addition of Zr and Mg on the microstructure and properties of a Cu–Cr–Sn–Zn alloy for etching lead frame

The effects on microstructure and properties of Cu–Cr–Sn–Zn with combined addition of Zr and Mg elements and their evolutions in the process of solid solution and thermomechanical treatment for etching high pin lead frames were studied. The microstructure was analyzed by OM, SEM, TEM, and EBSD. The results show that Cu–Cr–Sn–Zn and Cu–Cr–Sn–Zn–Zr–Mg alloys have the best performance after primary aging at 440 °C for 4 h and secondary aging at 400 °C for 4 h. The hardness and conductivity of the two alloys are 154 HV&78.3%IACS and 171 HV&77.8%IACS, respectively. Cu–Cr–Sn–Zn–Zr–Mg alloy final products shown better comprehensive performance, with conductivity, tensile strength, and hardness of 81.4%IACS, 580 MPa, and 175 HV respectively. The addition of Zr and Mg elements slows down the precipitation process of Cu–Cr–Sn–Zn alloy, refines the Cr phases, and inhibits the coarsening of Cr phases. Nano Cr clusters and coherent fcc Cr phases were observed during the aging process at 440 °C for 4 h and 400 °C for 4 h, which is difficult to observe in Cu–Cr–Sn–Zn alloy due to the precipitation and coarsening of Cr phases in a rapidly way. The surface roughness of Cu–Cr–Sn–Zn–Zr–Mg alloy without coarsened Cr phases is lower with Sa = 0.2681 μm.

Microstructure evolution and high-temperature tribological behavior of AlCrBN coatings with various B contents

The boron content affects the microstructures and high-temperature tribological performance of AlCrBN coatings. AlCrBN coatings with various B contents (0 at.%, 1.5 at.%, 2.9 at.%, 4.8 at.%,) were synthesized by multi-arc ion plating. The microstructure, mechanical and high-temperature tribological properties were investigated. TEM results show that addition of 1.5 at.% of B results in solid solution (Al, Cr, B)N and a small amorphous a-BNx within the (Al, Cr, B)N columnar structure. Further addition of B contents of 2.9 at.% and 4.8 at.% leads to the composite structure comprising of nano-grains surround by amorphous a-BN x . As the B content increases, the amount of nano-grains decreases, and the thickness of the amorphous layer increases. The hardness measurements also indicate that the AlCrBN coating with 1.5 at.% B content had the highest hardness of 38.3 GPa due to the solution strengthening. On the other hand the AlCrBN coating with 2.9 at.% B content had the best toughness with higher values of H / E (0.073) and H 3 / E * 2 (0.169 GPa). High-temperature tribological measurements showed that the friction coefficients decreased with temperature for all such AlCrBN coatings. At 400 °C, AlCrBN coatings with B contents of 0 at.%, 1.5 at.%, and 2.9 at.% exhibited low wear rates due to their high hardness, while AlCrBN coating with a B content of 4.8 at.% showed the lower wear rate at 800 °C due to the formation of a continuous B 2 O 3 /B(OH) 3 film on the coatings. • Microstructure of AlCrBN coatings is closely related with B contents. • Addition of 1.5 at.% of B results in the coherent fcc -BN/ fcc -AlCrBN interfaces. • Microstructures, mechanical and tribological properties were investigated. • Various friction oxide films depend on the different temperatures.

Ultra-high strength and plasticity mediated by partial dislocations and defect networks: Part I: Texture effect

Deformation mechanisms governing the strength of nanostructured metallic multilayers have been studied extensively. In general, size effect is the most effective way to tailor the mechanical strength of multilayers. Here we report that three Cu/Co multilayer systems with identical layer thickness but different types of layer interfaces exhibit drastically different mechanical behavior. In situ micropillar compression tests inside a scanning electron microscope show that coherent FCC (100) and (110) Cu/Co multilayer systems have low yield strength of about 600 MPa, and prominent shear instability. In contrast, the incoherent Cu/ HCP Co multilayers show much greater yield strength, exceeding 2.4 GPa, and significant plasticity manifested by a cap on the deformed pillar. Molecular dynamics simulations reveal an unexpected interplay among pre-existing twin boundaries in Cu, stacking faults in HCP Co, and incoherent layer interfaces, which leads to partial dislocation dominated high strength and outstanding plasticity. This study provides fresh insights for the design of strong, deformable nanocomposites by using a defect network consisting of twin boundaries, stacking faults and layer interfaces.

The phase transformation and strengthening of a Cu-0.71 wt% Cr alloy

Abstract The phase transformation of a Cu-0.71 wt% Cr alloy during the aging process at 450 °C was investigated by Transmission electron microscopy (TEM) and High-resolution transmission electron microscopy (HRTEM) in the study. The strengthening mechanism was studied as well. The precipitation sequence of Cu-0.71 wt% Cr aged at 450 °C is supersaturated solid sloution→G.P zones (fcc Cr-rich phase)→fcc Cr phase→order fcc Cr phase→bcc Cr phase. This transformation can be achieved by the nucleation of coherent fcc spherical precipitates and growth and transformation of fcc precipitates into the bcc structure. When the specimen is aged aging for 1 h–24 h, both fcc and bcc precipitates exist in the matrix simultaneously. Ordering process is found during the aging process, which is in favor of the precipitation of Cr-rich phases. The orientation relationship between bcc Cr precipitates and the matrix exhibit NW-OR. The peak strength effect occurs after aging for about 8 h and the strength continues to decrease with prolonging aging time, indicating overaging. The strengthening effect of Cr-rich phase precipitated in aging at 450 °C for 8 h is calculated to be 146 MPa on the basic of the Orowan strengthening mechanism, which is in quite accordance with the experimental data (144.5 MPa).

Stacking fault energy of face-centered cubic metals: thermodynamic and ab initio approaches

The formation energy of the interface between face-centered cubic (fcc) and hexagonal close packed (hcp) structures is a key parameter in determining the stacking fault energy (SFE) of fcc metals and alloys using thermodynamic calculations. It is often assumed that the contribution of the planar fault energy to the SFE has the same order of magnitude as the bulk part, and thus the lack of precise information about it can become the limiting factor in thermodynamic predictions. Here, we differentiate between the interfacial energy for the coherent fcc(1 1 1)/hcp(0 0 0 1) interface and the ‘pseudo-interfacial energy’ that enters the thermodynamic expression for the SFE. Using first-principles calculations, we determine the coherent and pseudo-interfacial energies for six elemental metals (Al, Ni, Cu, Ag, Pt, and Au) and three paramagnetic Fe–Cr–Ni alloys. Our results show that the two interfacial energies significantly differ from each other. We observe a strong chemistry dependence for both interfacial energies. The calculated pseudo-interfacial energies for the Fe–Cr–Ni steels agree well with the available literature data. We discuss the effects of strain on the description of planar faults via thermodynamic and ab initio approaches.

Microstructures and compressive properties of Ir-15Nb refractory superalloy containing nickel

Ni-based superalloys are among the most well known and successful materials in the history of the aeronautics and gas turbine industries. These superalloys exhibit a high and almost constant yield stress with increasing temperature, until a critical temperature is reached, above which the yield stress drastically decreases. Improving this critical temperature becomes increasingly difficult due to the low melting point of base nickel (Ni). Recently, the authors proposed a new class of refractory superalloys based on platinum group metals that are potentially useful at ultra-high temperatures, at which Ni-based superalloys can not be used. These refractory superalloys have coherent fcc and L1{sub 2} two-phase structures, higher melting temperature, and superior oxidation resistance. Preliminary results show that, of these refractory superalloys, Ir-15Nb was superior in high temperature strength and oxidation resistance. However, iridium (Ir) makes this refractory superalloy dense and expensive. Now, the challenge is to replace as much Ir as possible in Ir-15Nb, while still retaining its desirable properties. Ni is completely miscible with Ir in Ir-Ni binary alloy systems. In this study, the authors determined the effects of replacing Ir with Ni in Ir-15Nb by examining the compressive properties and microstructures of several Ir-15Nb-XNi alloys.

Quantum oscillations of properties in magnetic multilayers (invited)

An oscillatory interlayer exchange coupling observed in many sandwich and multilayer films can be understood as an interference effect of electron waves partially reflected at each interface with spin dependent reflection coefficients. Consequently, we might expect all magnetic properties in some way related to the density of states to oscillate as a function of the magnetic and nonmagnetic layer thickness. In order to experimentally test this concept we have measured different magnetic properties of Ni/Au multilayer films prepared by magnetron sputtering on glass substrates. The Ni thickness was kept constant at tNi=(7.3±0.5) Å while the Au layer thickness was varied between 4 Å and 80 Å. The films had a coherent fcc structure with (111) texture. The saturation field and the remanence oscillate as a function of tAu with a period which agrees well with a theoretical value calculated from the bulk Fermi surface of Au and proves that indeed an oscillatory exchange coupling is present. The Curie temperature shows oscillations with tAu clearly correlated with the exchange coupling constant, J: TC oscillates like the absolute value of J. This behavior is indeed expected from mean field theory. Similar oscillations are found for the spin wave parameter and the ground state magnetic moments. The variation of the exchange coupling with temperature and the role of inhomogeneities for the interpretation of the experimental data are discussed.

The phase of the oscillatory exchange coupling in coherent fcc (Fe-Co-Ni) / Cu (001) multilayers

The Cu thicknesses at which sputter-deposited coherent fcc (Fe-Co-Ni) / Cu (001) multilayers display the first, sharp, antiferromagnetic maximum in the interlayer exchange coupling were found to depend markedly on the ferromagnetic alloy concentration. The entire fcc part of the ternary Fe-Co-Ni system was investigated. The relevance to the theory of interlayer exchange is discussed.

Growth, structure, and physical properties of single-phase metastable fcc Cu1−xCrx solid solutions

Single-phase fcc-structure metastable Cu1−xCrx alloys have been grown with Cr concentrations of up to 23 at. %. The films, which were typically 1.5–3 μm thick, were deposited by rf co-sputter deposition onto glass and oxidized-Si substrates at temperature between 55 and 180 °C. The average grain size of alloys grown at 90 °C was ∼100 nm. The lattice parameter of Cu1−xCrx was found to increase linearly with x resulting in an effective fcc Cr radius, in solution, of 0.1332 nm. ∼7% larger than the elemental bcc Cr bonding radius. The room-temperature resistivity of these alloys also increased linearly with x at a rate of 2.8 μΩ cm per at. % Cr. This high differential resistivity was due, in addition to simple alloys scattering, to scattering of conduction electrons into virtual bound states associated with the Cr atoms. Cu0.9Cr0.1 alloys were found to be stable for 24-h anneals at temperatures up to ∼300 °C. From an analysis of x-ray diffraction peak positions and widths as a function of both growth and annealing temperatures, we conclude that the reaction path for the phase transition from the metastable to the equilibrium state involves first the precipitation of coherent fcc Cr particles followed by a transformation to bcc Cr as phase separation continues. The oxidation rate of Cu0.9Cr0.1 was found to be much less that that of pure Cu. At an annealing temperature of 250 °C, the oxide thickness tox on Cu0.9Cr0.1 saturated at J25 nm after 1 h while tox on Cu continued to increase parabolically with time from ∼60 nm at 1 h to 140 nm at 4 h.

Ferromagnetic ordering in fcc γ-Fe precipitates in Cu-Au alloys

While coherent fcc γ-Fe precipitates in a Cu matrix are ordered antiferromagnetically at low temperatures ( H int ≈ 23 kOe), precipitates in a Cu 69Au 30 matrix are ordered ferromagnetically ( H int = 208 kOe) as revealed by Mössbauer spectroscopy. Comparisons are made to epitaxial Fe films on Cu surfaces.

The Nature of the Barrier to Growth at Partially Coherent FCC:BCC Boundaries

The Nature of the Barrier to Growth at Partially Coherent FCC:BCC Boundaries

The structure of nearly coherent fcc: bcc boundaries in a CuCr alloy

In contrast to past investigations of dislocation structures at interphase boundaries, which have been confined largely to systems in which the atomic matching at these boundary orientations was obviously good, the present study was concerned with fcc:bcc boundaries, where the two lattices do not appear to match closely at any boundary orientation. Using the precipitation of Cr-rich bcc crystals from the fcc matrix of a Cu-0.33 wt% Cr alloy as a model system, however, well defined planar boundaries were often observed to develop in overaged samples. Transmission electron microscopic studies showed that such facets were invariably arrayed with one or two networks of parallel interfacial dislocations; within a given network, the dislocations were spaced from 100 to 1000 Å apart. Orientation relationship studies indicated a range of relationships varying from the Nishiyama-Wasserman to the Kurdjumow-Sachs; habit planes were usually irrational in both matrix and precipitate lattices. Most of these rather complex observations can be understood, however, if the (nominally) planar interfaces are modeled as sequences of steps whose broad faces are formed by {110} bcc//{111} fcc. By restricting the extent of the steps to regions of good fit between the two lattices, most of the misfit between them can be successfully accommodated. On this model, the interfacial dislocations play only a secondary role, serving to eliminate the residual mismatch accumulated within the systems of steps.