Coarsening kinetics of Cu-rich precipitates in a concentrated multicomponent Fe–Cu based steel (original) (raw)
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International Journal of Materials Research, 2008
The nucleation, growth, and coarsening kinetics of Cu-rich precipitates in a multicomponent Fe – Cu based steel, containing 1.17 at.% Cu, aged at 500 °C for up to 1024 h are investigated. The temporal evolution of the precipitate, heterophase interface, matrix compositions and precipitate morphology are presented. Coarsening temporal exponents are determined for mean radius, number density, and supersaturations, and are compared to the Lifshitz – Slyzov – Wagner model for coarsening, modified for multicomponent alloys by Umantsev and Olson. The experimental results indicate that the alloy does not strictly follow Umantsev – Olson model behavior. Additionally, we compare the results to an investigation of a similar multicomponent steel containing 1.82 at.% Cu and to results in the literature. Furthermore, we present a Thermo-Calc determined phase diagram.
The temporal evolution of the decomposition of a concentrated multicomponent Fe–Cu-based steel
Acta Materialia, 2008
The nucleation (to a limited extent), growth and coarsening behavior of Cu-rich precipitates in a concentrated multicomponent Fe-Cu-based steel aged at 500°C from 0.25 to 1024 h is investigated. The temporal evolution of the precipitates, heterophase interfaces, matrix compositions and precipitate morphologies are presented. With increasing time, Cu partitions to the precipitates, Ni, Al and Mn partition to the interfacial region, whereas Fe and Si partition to the matrix. Coarsening time exponents are determined for the mean radius, hR(t)i, number density, N V (t), and supersaturations, which are compared to the Lifshitz-Slyzov-Wagner (LSW) model for coarsening, modified for concentrated multicomponent alloys by Umantsev and Olson (UO). The experimental results indicate that the alloy does not strictly follow UO model behavior. Additionally, we delineate the formation of a Ni-Al-Mn shell with a stoichiometric ratio of 0.51:0.41:0.08 at 1024 h, which reduces the interfacial free energy between the precipitates and the matrix.
Compositional Variants of Cu-rich Precipitate in Thermally Aged Ferritic Steel
Acta Metallurgica Sinica (English Letters)
Atom probe tomography was utilized to investigate Cu precipitation in a high-strength low-alloy steel isothermally aged at 500°C for 1, 4, 16, and 64 h after water-quenching from 900°C. With prolonged aging time, the Curich precipitates (CRPs) increased in size and decreased in number density, and gradually evolved from spheroidal to elliptical in morphology. The small CRPs were rich in a high amount of Fe and a certain amount of Ni and Mn at their early nucleation stage. The large CRPs with increased size due to extensive aging contained less Fe and more Cu at their later growth stage. Additionally, Ni and Mn were both readily to segregate at the CRP/matrix heterophase interfaces, and Mn was higher in content than Ni in the precipitate interior especially when the CRPs were large in size. KEY WORDS: High-strength low-alloy steel; Thermal aging; Cu-rich precipitate; Atom probe tomography * 400°C [7-13]. Therefore, it is important to tailor the precipitation morphology of Cu-rich precipitates (CRPs) for attaining desired strength and toughness balance. Actually, the characteristics of CRPs in aspect of size, number density, shape, etc., that determine final mechanical properties are largely dependent of the compositional and resultant structural evolution during heat treatment process, and the segregation of Ni and Mn at the precipitate/matrix interface significantly prohibits the growth of CRPs to large size [14-21]. In additional, the compositional evolution of CRPs provides important information for composition modification, processing optimization, and property improvement of Cu-containing steels. However,
Atomistic computer simulation of the formation of Cu-precipitates in steels
Computational Materials Science, 2002
Thermal ageing of Cu-alloyed steels is a result of Cu-precipitates which arise above 300°C. Recently small angle neutron scattering was applied in order to analyse these precipitates in a defined initial state as well as in a thermally aged state. Atomistic computer simulations of the formation of precipitates can contribute to a deeper understanding of the mechanical behaviour of Cu-alloyed steels. A model is presented which is able to simulate the 'diffusion' of atoms by vacancy jumps . The underlying Monte Carlo method is presented and a binary system with components A and B is considered. Starting with a random distribution of atoms, the formation and growth of precipitates is simulated at a constant temperature of 600°C. In a second simulation, an initial temperature of 700°C is lowered to 400°C. At 700°C precipitates of radii between 1.1 and 1.7 nm are formed within seconds. At 400°C a part of the still dissolved atoms forms smaller precipitates while other atoms increase the size of the larger precipitates. At longer simulation times a significant decrease of the number of small precipitates and an increase of the averaged precipitate radius is found. The Russel-Brown theory is applied on the simulation results in order to calculate the increase of the yield stress in the thermally aged state. Ó
Early Stages of Precipitate Formation in a Dual Hardening Steel∗
HTM Journal of Heat Treatment and Materials, 2019
For plastic mold steels, secondary hardening as well as hardenable, corrosion-resistant steels are used. Secondary hardening can be achieved through alloying with Ni, Ti, Al and Cu. The precipitation sequence of combined Cu and intermetallic NiAl particles depends on the precise ratio of the alloying contents. In this study, a dual hardening iron-based alloy with a high ratio of Ni/Cu and Al/Cu and low Carbon content is investigated. These dual hardening steels represent alloys that utilize both carbidic and intermetallic secondary hardening precipitates to achieve secondary hardening. The investigations focus on the initial precipitation of intermetallic particles in order to analyze the sequence of precipitate formation for a specific ratio of alloying elements. DSC measurements were used to identify characteristic precipitation temperatures between 360 °C and 600 °C and the corresponding heat treatment conditions were reproduced using a quenching dilatometer. The initial stages o...
The influence of Cu addition on precipitation in Fe–Cr–Ni–Al–(Cu) model alloys
Ultramicroscopy, 2009
Precipitation in Fe-Cr-Ni-Al-(Cu) model alloys was investigated after ageing for 0.25, 3, 10 and 100 h at 798 K. Characterization of nanoscale precipitates was performed using three-dimensional atom probe microscopy and transmission electron microscopy. The precipitates are found to be enriched in Ni and Al (Cu) and depleted in Fe and Cr. After 0.25 h of ageing the number density of precipitates is $8 Â 10 24 m À3 , their volume fraction is about 15.5% and they are near-spherical with an average diameter of about 2-3 nm. During further ageing the precipitates in the both alloys grow, but the coarsening behaviour is different for both alloys. The precipitates of the Cu-free alloy grow much faster compared with the Cu-containing alloy and their density decreases. Precipitates in Cu-free alloy change to plate shaped even after 10 h of ageing, whereas those of Cu-containing alloy remain spherical up to 10 h of ageing. The influence of Cu addition on precipitation in these model alloys is discussed with respect to the different coarsening mechanisms.
Chinese Journal of Mechanical Engineering
High-dispersed nanoscale Cu precipitates often contribute to extremely high strength due to precipitation hardening, and whereas usually lead to degraded toughness for especially ferritic steels. Hence, it is important to understand the formation behaviors of the Cu precipitates. High-resolution transmission electron microscopy (TEM) is utilized to investigate the structure of Cu precipitates thermally formed in a high-strength low-alloy (HSLA) steel. The Cu precipitates were generally formed from solid solution and at the crystallographic defects such as martensite lath boundaries and dislocations. The Cu precipitates in the same aging condition have various structure of BCC, 9R and FCC, and the structural evolution does not greatly correlate with the actual sizes. The presence of different structures in an individual Cu precipitate is observed, which reflects the structural transformation occurring locally to relax the strain energy. The multiply additions in the steel possibly ma...
Coarsening kinetics of coherent precipitates in Ni-Al-Mo and Fe-Ni-Al alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1997
The late stage coarsening kinetics of coherent y' and ,B' have been investigated in single crystalline specimens of Ni-14.5 at.% Al-5.9 at.% MO and Fe-10 at.% Ni-15 at.% Al after aging at 14.53 K for the Ni alloy and 1233 K for the Fe alloy. Scanning electron microscopy (SEM) shows that early in the coarsening regime there is particle splitting in the Ni-base alloy. Continued aging changes the spatial distribution of particles giving rise to the formation of groups of many particles. In the Fe-base alloy. formation of particle groups is seen earlier. Longer agin g treatments produce large particles that split forming plate like precipitates. Particle migration is evident in both alloys. The coarsening kinetics of particles in the Ni-base alloy show deviations from the usual linear behavior between the cube of the average particle radius and the aging time. There is a reduction of the coarsening rate and in addition broader particle size distributions are obtained. In the Fe-base alloy, direct measurements of particle areas on SEM images show a linear dependence of the cube of the average particle radius with the aging time. However, after correcting for particle shape an increase of the coarsening rate is suggested. 8 1997 Elsevier Science S.A.