Formation Of Coherent Precipitates Research Articles

Optimized rolling processes to balance magnetic and mechanical properties of high-strength non-oriented silicon steels

A bottleneck in the development of high-strength non-oriented silicon steels for drive motors of new energy vehicles is the balance of strength and magnetic properties. This paper successfully tackled this problem through the optimization of thickness reduction for hot and cold rolling and the formation of coherent precipitates using a Cu-alloyed non-oriented silicon steel. More specifically, a thickness reduction of 96% in the course of hot rolling promoted the homogenization of microstructure during the following normalization treatment. Subsequently, a deformation degree of 80% during cold rolling ensured the inheritance of the uniform microstructure and inhibited the abnormal growth of recrystallized grains during annealing, thereby suppressing the iron loss to a value as low as 15.6 W/kg. At the meantime, this combined process promoted the inheritance of λ-fibers and the formation of {114}〈481〉 texture in the annealed sheet, improving the magnetic induction intensity B50 to 1.606 T. In addition, under the joint effect of a variety of strengthening mechanisms, the yield strength of this annealed sheet reached 668 MPa. A pronounced increase in strength, about 207 MPa, was derived from precipitation hardening by the great difference in the modulus between coherent Cu-rich clusters and the α-Fe matrix.

Development of coherent-precipitate-hardened high-entropy alloys with hierarchical NiAl/Ni2TiAl precipitates in CrMnFeCoNiAlxTiy alloys

Coherent precipitates hardening is currently emerging strengthening mechanism of the various high entropy alloys (HEAs). Recently, CrMnFeCoNiAlx HEAs have been studied to show a phase transition from face-centered-cubic (FCC) to body-centered-cubic (BCC) and formation of coherent precipitates (B2-NiAl) within the BCC matrix. The coherent precipitates in the CrMnFeCoNiAlx alloys could contribute to increase the strength but lead to considerable reduction of the ductility. The present work systematically investigated a series of CrMnFeCoNiAl0.5Tix alloys to further improve the strength and plasticity, as compared to the previously reported CrMnFeCoNiAlx HEAs. As a result, an increase of Ti addition leads to the phase transition from FCC to BCC and formation of lamellar structure and hierarchical precipitates reinforced by B2-NiAl and L21-Ni2TiAl phases. Excellent mechanical properties were achieved from CrMnFeCoNiAl0.5Ti0.1 and CrMnFeCoNiAl0.5Ti0.2 alloys. The mechanical properties of the CrMnFeCoNiAl0.5Tix alloys were discussed via theoretical strengthening mechanisms.

Influence of Interface Proximity on Precipitation Thermodynamics

The formation of coherent precipitates is often accompanied by large elastic mismatch stresses, which suppress phase separation. We discuss the presence of interfaces as a mechanism for stress relaxation, which can lead to preferred zones of precipitation. In particular, we discuss the proximity of free surfaces and shear-coupled grain boundaries, for which we can obtain a substantial local energy reduction and predict the influence on the local precipitation thermodynamics. The latter case is accompanied by morphological changes of the grain boundary, which are less suitable for large-scale descriptions. For that purpose, we develop an effective description through an elastic softening inside the grain boundary and map the microscopic grain boundary relaxation to a mesoscopic elastic and phase field model, which also allows generalizing the description to multi-phase situations.

Vacancy‐solute association in coherent nanostructures formed in a commercial Al‐Zn‐Mg‐Cu alloy

AbstractThe role of vacancy‐solute association in the formation of coherent precipitates at room temperature (RT) and at 70 °C was studied by means of coincidence Doppler broadening (CDB) spectroscopy. The formation of clusters and GP zones was monitored by differential scanning calorimetry (DSC). Two conditions were explored at low temperature: a) one‐step aging after solution treatment and quenching and b) secondary aging (after solution treatment and quenching + 5 days at RT + 8 min at 150°C). The assessment of the average fractional concentration of solute in contact with the vacancies was obtained by analyzing the CDB data. The results show considerable aggregation of Cu to vacancies at the very early stage of decomposition of the supersaturated solid solution; the contribution of Zn and Mg increases progressively with the formation of coherent precipitates. The preliminary exposure at 150 °C does not alter this sequence, although a reduction in the dissolution enthalpy observed during DSC scans shows retarded formation of coherent precipitates. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Implantation of group IVA elements in TiO 2: lattice site location and diffusion

Ge-, Sn- and Pb-ions with oxidation state +4, similar to that of Ti, were implanted into rutile single crystals. Ion profiles and lattice site location were determined by Rutherford-backscattering and channeling. Previously it was noted that the widths of the angular dip curves for Ge and Sn were wider and deeper than those of Ti, indicating the formation of coherent precipitates, while Pb atoms were displaced along the c-axis. Annealing at high temperatures caused the impurities to move to regular substitutional Ti lattice sites. The influence of diffusion effects on the lattice site occupation and on the formation of precipitates has been studied here in more detail for aligned and randomly oriented implants. For aligned implants Sn-diffusion occurred between 850 and 950 K, about 200 K below the temperature region where diffusion is observed for random implants. The steep decrease of the Sn peak area without broadening indicates that the diffusion is governed by trap release. The local damage density near the impurity at the end of the ion track seems to play a big role: for aligned implants the diffusion occurs in the temperature region where the damage anneals, while for random implants ion diffusion is not connected to damage annealing and occurs due to a substitutional process via cation lattice sites.

Precipitation behavior in Ti25AlH x alloys

A number of studies have been conducted on Ti-Al-H or Ti-Al-M-H (M = metallic addition) alloys. However, no comprehensive studies of the ternary Ti-Al-H system have been carried out. In the present work, hydrogen solubility and precipitation in binary Ti{sub 3}Al was investigated as part of a study of the Ti-Al-H system. The formation of coherent precipitates in Ti-25Al (at%) is reported in this paper.

Effects of Spallation neutron irradiation on single crystals of Iron, Nickel, Niobium and Stainless Steel

Abstract Single crystals of Iron, Nickel, Niobium and Stainless Steel (SS316) subjected to prolonged neutron irradiation in the Los Alamos Spallation Source for a period of one year have been studied using both small angle, and single crystal neutron diffraction. Small Angle Scattering show no evidence of any large radiation induced inhomogeneities in the pure metals, while regions of ∼ 65 A diameter are found in the irradiated SS316. Combining the s.a.s. measurements with the single crystal diffraction data these regions are attributed to the formation of coherent precipitates of Ni-Cr. However, a low concentration of point defects (<2.5 at %) is introduced in all the materials by the irradiation process. No significant radiation induced dilatation of the lattice is found in any of the materials.