Precipitation Behavior Of Phase Research Articles

Effect of Aging Precipitation Behavior of Ti2Ni Phase on Compressive Properties of 54NiTi Alloy

Effect of Aging Precipitation Behavior of Ti2Ni Phase on Compressive Properties of 54NiTi Alloy

Effect of heat treatment on microstructure, precipitation behavior and mechanical properties of Inconel 718 fabricated by laser direct energy deposition

The uncontrollable directional grain growth and non-equilibrium microstructure of Inconel 718 will form during laser direct energy deposition (LDED), which seriously limits the promotion and application, so it is necessary to consider the heat treatment to improve the microstructure and mechanical properties. In this paper, the effects adopting different heat treatments on the phase composition, precipitation behavior, grain structure, tensile and tribological properties of LDED Inconel 718 have been systematically investigated, with as-deposited samples compared. The results show that the number and size of γ″ phases can be significantly changed under different aging and solution conditions, and the strength and wear resistance increase while elongation decreases since the fine grain and precipitation strengthening occurring during heat treatment. By comparing the different samples, the SA1100A exhibits the highest yield and tensile strength, with 140.6% of yield strength and 83.9% of ultimate tensile strength increasing compared to as-deposited samples, also showing the narrowest wear mark width and the lowest average mass loss.

Continuous precipitation behavior of Mg17Al12 phase during multiple steps of twinning-aging procedure in Mg-Al alloys

Twinning was regarded as an effective way to modify the precipitation in Mg alloys. Two procedures were designed to illustrate twinning-aging consequence on Mg17Al12 phase evolution. The effect of multiple steps of twinning-precipitation on the morphology and density of the continuous precipitates inside the twins and the matrix were comprehensively analyzed through phase-orientation related observation. The results show the shape of precipitates in twins was similar to that in the matrix as the CPs mostly lay on the basal planes with an asymmetric-lozenges shape. The CPs were remarkably refined and its density became much higher inside twins. Moreover, the aspect ratio of the CP plates in twins was around 45% of that in the matrix, which means the CPs inside twins became more globular. The precipitation behavior of Mg17Al12 phase inside double extension twins was different from the primary twin or the matrix. The Mg17Al12 phases lay on both basal and prismatic planes can be observed in double twins of two-step precipitation. The growth behavior of pre-precipitates in twins is different from those in the matrix. The growth rate along its thickness became higher than that in the matrix, which is probably related to dislocation-assisted diffusion at the basal plane.

Effect of Mo on the σ-phase precipitation behavior of super-austenitic stainless steel

The aging precipitation behavior of super-austenitic stainless steels 904L (4.32% molybdenum (Mo)), 254SMo (6.06% molybdenum) and AL-6XN (6.29% molybdenum) with different molybdenum contents at 800–900°C was investigated by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The effect of molybdenum content on the σ-phase precipitation behavior of commonly used super-austenitic stainless steel was investigated. The results show that the super-austenitic stainless steels with different molybdenum contents formed different numbers and shapes of σ phases in the isothermal aging process, and the number of σ phases of 254SMo and AL-6XN is much larger than that of 904L, and the shape of the σ phases mainly shows coarse acicularity and elongation, while the σ phases of 904L show fine granularity.

Effect of Al addition on Nb-rich phase precipitation behavior in ferritic stainless steel

The precipitation behavior of Nb-rich phase in Al-free and 1Al Nb-bearing ferritic stainless steels (FSSs) at 700 °C were investigated. The results show that Nb-bearing carbides and Laves phases with mutual transformation relationships are precipitated in both Al-free and 1Al Nb-bearing FSSs at the early stage of aging. At this stage, the coarsening rate of Laves phase is higher than that of Nb2C phase, and the addition of Al can promote the precipitation of Laves phase and weaken the precipitation of (Nb, Ti)2C phase. As the aging time extended to 60 min, the Nb-rich phase in the two experimental steels was mainly Laves phase, and the intragranular Laves phase showed feather like aggregation distribution. On the one hand, the added Al can be enriched in the Laves phase to produce a tailing morphology, on the other hand, it can reduce the diffusion rate of Nb atoms in the matrix, thereby weakening the aggregation state of the intragranular Laves phase. During the coarsening process of Laves phase, the addition of Al can reduce the coarsening rate of Laves phase by 7.45 times.

Study of ordered phase precipitation behaviour and hardening mechanism of Au-20Ag-10Cu alloy during deformation-aging treatment

With the rapid development of aerospace technology, the demand for a longer service life of Au-Ag-Cu alloy as conductive slip rings is increasing. Therefore, it is important to improve the hardness of the alloys in order to prolong their service life. Deformation-aging can improve the hardness of many alloys. The effect of the deformation-aging process of Au-20Ag-10Cu (wt%) alloy was investigated on the microstructure and properties, which characterized by DSC(Differential Scanning Calorimeter), XRD(X-ray Diffraction), EBSD(Electron Backscatter Diffraction), TEM(Transmission Electron Microscope) characterization techniques, microhardness and electrical conductivity testing methods. The results indicated that the microhardness increases and the conductivity decreases gradually with the increase of deformation rate. As the aging time increasing, the content of face-centered tetragonal AuCu I ordered phase increases, and thus the hardness increases gradually. The maximum hardness value of 307.44 HV was obtained after undergoing 70 % deformation and then aged at 300 ℃ for 16 h with the electrical conductivity values of 8.40 MS·m−1. This result indicated that both higher hardness and higher electrical conductivity of Au-20Ag-10Cu (wt%) alloy could be obtained, which ensures the requirements in the field of electrical contact materials.

Tailoring the brittle phase precipitation and mechanical properties in developing ultra-super ferritic stainless steels by Al modification

An isothermal ageing experiment was carried out to investigate the influence of Al modification on the brittle phase precipitation behaviour, grain coarsening and mechanical properties of newly designed ultra-super ferritic stainless steel. Experimental results demonstrated that the modification of Al significantly inhibited the formation rate of the sigma phase, retarded the induction period of the chi phase, and promoted the growth process of the Laves phase. Meanwhile, the calculated grain growth kinetics of the surface layer and core layer were compared with the measured values. It was found that the Al modification enhanced the effect of Laves phase precipitation pinning and solid solution drag, which slowed the grain coarsening rate. With the modification of Al, the values of ultimate tensile strength, yield strength (0.2% proof stress) and total elongation increased compared to those of the Al-free alloys. The plasticity of the Al-modified alloys was improved with the retardation of sigma and chi phases at the grain boundary. This study provided valuable insights for the development of Al-modified ultra-super ferritic stainless steels with low precipitation brittleness tendency.

Microstructure evolution and precipitation behavior of hot-rolled high-strength Ti–Mo–V micro-alloyed steel

The microstructure evolution and precipitation behavior of hot-rolled Ti–Mo–V micro-alloyed high-strength steel processed at different final rolling temperatures (FRT) and coiling temperatures (CT) were investigated. The results indicated that the decrease of FRT (880 °C–820 °C) promoted the ferrite refinement and strain-induced precipitation in austenite, but it also led to the decrease of pearlite content, which finally led to a slight difference in properties, and CT obviously changed the phase component, grain size, and precipitation behavior. Appropriate reduction of the CT (650 °C–600 °C) could promote the precipitation of (Ti, Mo, V)C and refine ferrite grains, thus improving strength. As the CT further lowered to 550 °C, the precipitation hardening effect would be seriously lessened owing to the significant reduction of (Ti, Mo, V)C volume fraction, finally resulting in the loss of strength. The optimum mechanical properties were attained for the FRT850-CT600 sample, and the ultimate tensile strength (UTS), yield strength (YS), and total elongation (TE) were 908 MPa, 848 MPa, and 21.5 %, respectively, with precipitation hardening up to 383.51 MPa.

Effect of heat treatment on precipitation behavior of second phase and property evolution of martensitic stainless steel

The microstructural optimization for 15–5PH stainless steel by heat treatment to enhance toughness and corrosion resistance were investigated. The results indicate that Cu-rich nanoparticles with a size of less than 30 nm are homogeneously dispersed within the matrix, exhibiting a K-S orientation relationship with the martensite matrix during the aging treatment. Additionally, reversed austenite is found to be distributed at the martensite lath boundaries, with the maximum content of 1.62% being observed at 550 °C. With increasing aging temperature, the dispersion strengthening effect caused by the precipitation of Cu-rich phases gradually weakens. After immersion in a 6% FeCl3 solution for 12 h, the greatest weight loss is observed in the 600 °C treated samples, followed by those treated at 450 °C, 550 °C, and 1050 °C.

High-precision Cu alloy microlattices with superior energy absorption capacity enabled by nanoprecipitation engineering

Printing of thin-wall copper alloy components with high mechanical performance using selective laser melting remains challenging. Here, the introduction of the soft Cr nanoprecipitations via increasing the Cr to Nb atomic ratio based on commercial CuCrNb alloys can suppress the excessive formation of Cr2Nb Laves phase and enhance the deformability of CuCrNb microlattices. Small printing layer thickness contributed to the high-density and small-size nanoprecipitations. Dual nanoprecipitations strategy enables us to successfully fabricate high-precision CuCrNb microlattices with the feature size down to 100 µm and exceptional printability, high mechanical strength, and homogeneous deformability until densification strain. By tailoring the precipitation behavior of Cr phase at post-printing stage, CuCrNb microlattices can further enhance the mechanical performance. Our peak-aged Gyroid CuCrNb microlattice displays an ultrahigh specific energy absorption of 23 J/g without fracture at strain above 60 %, even surpassing that of some titanium and aluminum alloys lattice structures with low material densities.

Precipitation Behavior and Corrosion Properties of Stirred Zone in FSWed AA5083 Al-Mg Alloy after Sensitization

This paper investigated the Mg-rich phase precipitation behavior and the corrosion performance throughout the thickness direction within the stirred zone (SZ) of friction stir welded (FSW) AA5083 alloy after 175 °C/100 h sensitization. For the as-welded SZ, the recrystallized grain size gradually decreased from the top surface (5.5 μm) to the bottom (3.7 μm). The top and bottom of the SZ maintained relatively high levels of deformed grains and accumulated strain induced by either shoulder pressing or pin stirring. After 175 °C/100 h sensitization, 100 nm thick β′-Al3Mg2 precipitates were present along the grain boundaries (GBs) in the SZ. The bottom of the SZ exhibited more continuous precipitates along GBs due to the fine grain size and the large fraction of high-angle grain boundaries (0.724%). Although the as-welded SZ exhibited excellent corrosion resistance, it became extremely vulnerable to intergranular cracking (IGC) and stress corrosion cracking (SCC) after sensitization. The large SCC susceptibility indices of the SZ samples ranged from 66.9% to 73.1%. These findings suggest that sensitization can strongly deteriorate the corrosion resistance of the Al-Mg FSW joint, which is of critical importance for the safety and reliability of marine applications.

Evolutionary mechanism of the precipitation behavior and organization of iron-containing intermetallic phase during solidification of recycled high-Fe Al-Zn-Mg-Cu melts

The remelting of aluminum scraps can result in the accumulation of impurities, with iron being the most prevalent among them. The presence of such impurities can cause downgrading and hindered utilization of the material. Despite this, the evolution mechanism of the Iron-containing Intermetallic Phase (IIP) in recycled high-Fe and low-Si aluminum melt has received limited attention and requires further investigation. This study investigates the evolution mechanism underlying the precipitation behavior and organization of the IIP during the solidification process of recycled high-Fe Al-Zn-Mg-Cu melts, utilizing a combination of simulation and experiment. Our findings indicate that the precipitation behavior of the high-temperature precipitation phase (HPP) in the melt is influenced by the Mn and Si, which subsequently determines the organization of the IIP. Specifically, the predominant forms of IIP in the recycled high-Fe Al-Zn-Mg-Cu alloys are lamellar and hollow rod-like phases with anisotropic, as well as skeletal phases with isotropic organization. Moreover, the synergistic addition of Mn and Si can increase the precipitation temperature (PT) and precipitation temperature interval (PTI) of the Al15(Fe,Mn)4Si2 phase in the melt, leading to the transformation of the IIP into a skeletal organization that can be easily removed and has less impact on the material properties. These findings provide insights into alloy design strategies aimed at minimizing the impact of iron accumulation on the cycle life of aluminum scraps and the performance of recycled aluminum.

Enhancing fine-scale α phase precipitation and mechanical behavior by addition of Cu to metastable β Ti-5553 alloy

Metastable β Ti alloys in the β quenched condition exhibit relatively low mechanical strength. Aging heat treatment can improve mechanical strength because of controlled α phase precipitation into the β matrix. This study aimed to examine the aging response of a β quenched Cu-modified Ti-5553 alloy, α phase precipitation therein, and the resulting mechanical behavior. It was found that Cu addition resulted in the precipitation of a nanometric Ti2Cu intermetallic compound, which upon aging, affected α phase precipitation and therefore increased the ultimate tensile strength from 1147 to 1222 MPa at the expense of ductility.

Effect of Ni-based Fillers on Corrosion Resistance of Heat Affected Zone of Super Austenitic Stainless Steel (UNS S31254) Welded by GTAW

The effect of Ni-based fillers on corrosion resistance of welded super austenitic stainless steel (SASS) was examined. The use of Ni-based fillers for gas tungsten arc welded SASS leads to the formation of fine Cr-Mo enriched phase in its weld unmixed zone, which makes it more susceptible to the localized corrosion. The metallographic observations showed that the pits were initiated around the fine Cr-Mo enriched phase precipitated in unmixed zone, and they were propagated along the base metal. The degree of corrosion damage among the welded samples using the three types of Ni-based fillers (Inconel 625, Inconel 622, Hastelloy 276) increased with the Mo contents in the fillers applied. The higher the Mo contents in the fillers, the higher the size/number ratio of Cr-Mo enriched phase with higher concentration of Mo, precipitated in unmixed zone. Based on the results, it is proposed that the Mo contents in Ni-based high alloyed fillers can have a great effect on the precipitation behavior of Cr-Mo enriched phase in unmixed zone, causing deterioration of corrosion resistance of SASS welds. Therefore, the Mo content in the filler should be optimized with the content similar to that of the base metal so as not to susceptible to localized corrosion.

Enhanced thermoplasticity of 7Mo-0.4 N contained super austenitic stainless steel through pre-deformation

This study investigated the hot tensile deformation behavior of super austenitic stainless steel (SASS) with different pre-deformation degrees within 1150–1250 ˚C. The influence of pre-deformation on the number of annealing twin (AT), grain size, dislocation evolution, sigma phase precipitation, static recrystallization (SRX), and dynamic recrystallization (DRX) behaviors at hot tensile deformation stages is analyzed. Results show that the thermoplasticity of the SASS increases first and then decreases with the increase of pre-deformation degree at each deformation temperature. The area reduction of the samples pre-deformed for 0 %, 10 %, 20 %, and 25 % are 0.25, 0.32, 0.37, and 0.35, respectively at a tensile temperature of 1150 ˚C. When the pre-deformation degree is within the range of 0–20 %, the deformation storage energy (DSE) gradually increases with the pre-deformation degree. The SRX amount at the high-temperature holding stage and the DRX amount in the high-temperature deformation stage significantly increases, and the grain size gradually decreases. As a result, crack initiation and propagation are inhibited, and thermoplasticity improves. However, when the pre-deformation degree is increased to 25 %, the grains grow abnormally during the high-temperature tensile deformation, and a large number of sigma phases are induced, which deteriorates the thermoplasticity of the SASS.

Influence of Nb content on phase precipitation behavior of new Ni–Co-based superalloys by selective laser melting

In this paper, the evolution of the γ′ and η phases of new Ni–Co-based superalloy with different Nb contents was investigated using a combination of thermodynamic calculations and high-throughput selective laser melting (SLM). Thermodynamic calculations show that the increase of Nb content lowered the solubility temperature of the γ′ phase and caused the precipitation of the η phase. The alloys with the Nb gradient content prepared by SLM during aging at 800 °C for 100h indicated that the maximum volume fraction and size of the γ′ phase reach the maximum at 3.0–3.5% Nb. The elongated η phases enrichment in Ni, Ti, and Nb atoms precipitate for the Nb content higher than 2.2% Nb and prefer to grow longitudinally at the expense of the γ′ precipitates. Combining the influence of the Al/(Nb + Ta + Ti) ratio on the η precipitates, the addition of Nb content in the Ni–Co-based superalloys is less than 2.2%, which increases the high-temperature yield strength and tensile strength.

Effects of Welding Parameters on Sigma Phase Precipitation in 25Cr-5Ni-1Mo-2.5Cu-1Mn-0.18N Duplex Stainless Steel

Recently, a new grade of duplex stainless steel, UNS S82551 (25Cr-5Ni-1Mo-2.5Cu-0.18N), has been developed to overcome the drawbacks in super martensitic stainless steel, conventional 22Cr and 25Cr super duplex stainless steels in terms of productivity and cost. The characteristic of the alloy design of UNS S82551 is to use Cu, instead of Mo, to ensure comparable corrosion resistance and strength. In addition, due to the significant decrease in Mo content, UNS S82551 is expected to be less sensitive to sigma phase precipitation during single or multi-pass welding compared with conventional and super duplex stainless steels. There is a trade-off between achieving better properties and avoiding sigma phase precipitation when increasing alloying elements such as Mo, Cr and Cu. In order to utilize the new UNS S82551 steel in industry for welding in a similar manner to conventional and super duplex stainless steels, the prevention of sigma phase precipitation is important. This work investigated the effect of weld thermal cycling on sigma phase precipitation behaviour in UNS S82551 welds. During thermal cycling in the tests, the amount of sigma phase for UNS S31803 and UNS S32750 increased with increasing the number of thermal cycles, and lower cooling rate, but it was not observed for UNS S82551. Based on the isothermal kinetics of sigma phase precipitation, the amount of sigma phase precipitated during thermal cycle can be predicted by applying the additivity rule to the physical model. The area fractions of sigma phase calculated have a good fit to the experimental ones.

A novel precipitation mechanism of Laves phase in Fe-30Cr-2Mo super ferritic stainless steel: In-situ phase transformation

Laves phase is generally prejudicial to the performance of ferritic stainless steels, so understanding the underlying formation mechanism should be technologically useful. Here we demonstrate a new precipitation behavior of Laves phase in Fe-30Cr-2Mo super ferritic stainless steel by using transmission electron microscopy. It is revealed that the MC carbides firstly precipitate adhere to the M2SC carbosulphides with an orientation relationship (OR) of (0001)M2SC//(111¯)MC and [112¯0]M2SC//[011]MC. Subsequently, the interfaces between MC carbides and ferrite matrix provide preferential nucleation sites for Laves phases, which hold OR with MC as follows: (111¯)MC//(0003)Laves and [011]MC//[112¯0]Laves. Notably, the transformation from MC to Laves phases is an in-situ process based on the dissolution of MC carbide, which supplies the niobium element for nucleation and growth of Laves phase. This work enriches the recognition of the precipitation mechanism of Laves phase, and should therefore facilitate the design of high-performance ferritic stainless steels.

Tailoring Microstructure of Austenitic Stainless Steel with Improved Performance for Generation-IV Fast Reactor Application: A Review

Austenitic stainless steels are selected as candidate materials for in-core and out-of-core components of Generation-IV fast reactors due to their excellent operating experience in light-water reactors over several decades. However, the performance of conventional austenitic stainless steels proves to be inadequate through operation feedback in fast reactors. To withstand the demands for material performance exposure to the extreme operating environment of fast reactors, modified austenitic stainless steels for in-core and out-of-core components have been developed from the first-generation 300-series steels. The design of an appropriate microstructure becomes a top priority for improving material performance, and key metallurgical features including δ-ferrite content, grain size and secondary phase precipitation pertinent to austenitic stainless steel are focused on in this paper. δ-ferrite content and grain size are closely correlated with the fabrication program and their effects on mechanical properties, especially creep and fatigue properties are critically assessed. Moreover, the impacts of some major elements including nitrogen, stabilization elements (Nb, Ti, V), phosphorus and boron on secondary phase precipitation behaviors during aging or creep are reviewed in detail. Based on the role of the aforementioned metallurgical features, the recommended specification of nitrogen content, stabilization ratio, phosphorus content, boron content, δ-ferrite content and grain size are put forward to guarantee the best-expected performance, which could provide reactors designers with attractive options to optimize fast reactor systems.

Laves Phase Precipitation Behavior in HiperFer (High Performance Ferritic) Steel with and without Boron Alloying

High-chromium ferritic stainless HiperFer steels were developed for high-temperature applications in power conversion equipment. The presented research describes the precipitation behavior of the Laves phase after the thermomechanical treatment of Fe-17Cr-0.6Nb-2.4W HiperFer alloys with and without the addition of 55 ppm boron. The boron-alloyed variant was produced with the aim of enhancing grain boundary strengthening and consequently increasing creep resistance. The focus is set on the effect of boron on the thermomechanically induced precipitation of (Fe,Cr,Si)2(Nb,W) Laves phase at grain boundaries. The addition of boron modifies the diffusion conditions in the area of grain boundaries. Consequently, the formation of Laves phase is promoted and the particle growth and coarsening process are suppressed. The impact of boron addition was validated by performing creep and thermomechanical fatigue testing in the standard processing state of HiperFer steel. In the B-alloyed variant, increased creep ductility through the modification of the particle-free zone widths at high-angle grain boundaries was encountered. Nevertheless, an optimized thermomechanical treatment is necessary to fully utilize the increased ductility effect for the creep strength optimization of the B-alloyed grade.