Si Solid Solution Research Articles

Influence of Si-addition on tribological and corrosion properties of Ta-Si-C coatings

Ta-Si-C coatings with Si content varying from 2.7 to 30.8 at.% were synthesized by magnetron co-sputtering. Their microstructure, tribological properties and corrosion performance were investigated. The coatings exhibited two distinct structural forms: a Ta(C, Si) solid solution for the lower silicon contents (2.7 and 5.6 at.% Si) and a Ta(C, Si)/a-C:Si nanocomposite for higher Si content (13.7, 20.8 and 30.8 at.% Si). Notably, the Ta(C, Si) solid solution at 5.6 at.% Si demonstrated the highest hardness of 44±2.7 GPa, resulting from the solid solution strengthening. Furthermore, this solid solution also demonstrated the lowest wear rate (1.21×10-6 mm3N-1m-1), due to its superior hardness and H3/E2 ratio. Additionally, the coating with 5.6 at.% Si displayed the most outstanding corrosion resistance, attributed to its higher crystalline quality and denser structure, which effectively prevented the permeation of corrosive media through the coating to the substrate.

Synthesis and tribological characterization over a wide temperature range for A-site elements doping in Ti3AlC2

This work investigates the possibility of doping Si and Sn solid solution components (separate/simultaneous incorporation) into Ti3AlC2 to provide desired mechanical properties and tribological self-adaptability over a broad temperature range. The specimens are sintered at 1450 °C for 2 h in a vacuum environment with a pressure of 30 MPa. The phase composition, mechanical properties and tribological characteristics sliding against Al2O3 counter balls over a wide temperature range from room temperature to 800 °C are investigated. The results demonstrate considerable lattice distortion together with significant solid solution strengthening effects in quinary solid solutions. The friction coefficients of the four solid solutions are discovered to be temperature-sensitive from the distinguished variation tendencies in the wide temperature range. The wear rates exhibit a comparable tendency with test temperature that the values are two orders of magnitude lower at 600−800 °C than those at RT−400 °C. The noticeably lubricant tribofilm is responsible for the decreased wear rate at elevated temperatures. The distinct tribological behaviors of the quaternary and quinary solid solutions are ascribed to the characteristics of the self-generated oxides.

Effect of Si and Y solution on mechanical properties of 30Cr13 martensitic stainless steel

The effect of alloying element silicon (Si) on yttrium (Y) solid solution in steel has been studied by anhydrous electrolysis experiment and first-principles calculation. The effect of Y and Si solid solution on the mechanical properties of steel were studied by tensile and hardness test. The influence mechanism was analyzed by geometry and electronic structures. The results show that Si can promote Y solid solution in steel. Since the Fe–Y bond energy was less than the Fe–Fe bond, the elastic properties of Fe were reduced by adding Y. The extremely high density of electron clouds around Si improves some of the elastic properties of Fe–Y–Si. Compared with Fe, the Young ‘s modulus of Fe–Y–Si sample was decreased by 4.3 GPa and the hardness of Fe–Y sample was increased by 4.22 HV. Y reduced the interaction of the slip surfaces and Si enhanced it, thus changing the plasticity of the steels.

On the properties of cast and powder metallurgical Cu–6Ni-1.5Si-0.15Al (wt.%) alloy

In this study, Cu–6Ni-1.5Si-xAl (x = 0 and 0.15 wt%) alloys are manufactured as billet materials by casting and their metallurgical and physical properties are characterized. Aluminum modified alloy is obtained also by a powder metallurgical (PM) route and its structural properties are determined to be compared with the cast materials. The findings indicate that (i) solidified alloys have distributed nickel silicides (27.01 %) embedded in α-Cu(Ni,Si) solid solution, (ii) the addition of aluminum increases the amount of silicides (29.09 %) in the solidified matrix and reduces both the grain size and the secondary dendrite arm spacing, (iii) although PM alloy has similar microstructural features as cast alloys, it exhibits the highest hardness (159 HV1) due to both finer grain structure and better distribution of silicides, (iv) both impurity and porosity have a determining effect on the electrical conductivity (27–32 % IACS, International Annealed Copper Standard) values of the alloys.

Self‐lubricating effect of solid solution elements on tribological performance of Ti3AlC2 over a wide temperature range

AbstractThis study explores the feasibility of tribological self‐lubricating over a wide temperature range by doping Si and Sn solid solution components on the A‐sites of Ti3AlC2 to adapt to the severe circumstances. The specimens were sintered at 1450°C for 120 min under a pressure of 30 MPa in a vacuum environment, and their dry sliding tribological capabilities against Al2O3 at temperatures ranging from ambient temperature to 800°C were investigated using a rotational ball‐on‐disk tribo‐tester. The findings demonstrated a constantly decreased friction coefficient of Ti3Al0.8Si0.2Sn0.2C2 throughout the temperature range and admirable antifriction at higher temperatures where wear rates were 1–2 orders of magnitude lower than those at room temperature, which was superior to earlier reported Ti3AlC2. The predominant friction surface self‐adaptability mechanisms after solid solution treatment were determined to be tribo‐oxidation wear and tribo‐chemical reactions that played a vital role by examining the microstructural evolutions and tribo‐chemical phase composition on friction surfaces at various temperatures. The tribo‐oxidation‐induced generated lubricant film consisting of TiO2, Al2O3, SnO2 mixture oxide phases, and aluminosilicates was responsible for the decreased friction coefficient and wear rate.

First-principles study on the high-strength and high-conductivity modification mechanism of C7035 copper alloy by Ni, Si, and Co solid solution

In order to investigate the effects of matrix solid solution, precipitate phases, and microscale interfaces on the mechanical and electrical properties of copper alloys, we employed first-principles calculations based on density functional theory study aimed to understand how alloying elements enhance the strength and conductivity of copper. The results demonstrated that doping Co atoms into the copper matrix using the Dop2 structure model exhibited the most significant improvement in both mechanical and electrical properties. The Young's modulus was doubled compared to pure copper, and the hardness increased several times. The electrical conductivity reached 59.8 % of the International Annealed Copper Standard (IACS), showing a 6.6 % enhancement compared to Si doping. To validate computational results, we conducted experiments that confirmed the accuracy of the predicted mechanical and electrical properties. Furthermore, the introduction of Co effectively reduced electron losses at the interface between the precipitate phase and the copper matrix. The electron transmission rate through the Co2Si (211)/Cu (111) interface reached 78.6 %, representing a 94.1 % improvement compared to the Ni2Si (111)/Cu (111) interface. In conclusion, Co can simultaneously enhance the mechanical and electrical properties of Cu–Ni–Si alloys, providing theoretical guidance for the design and fabrication of high-strength and high-conductivity copper alloys.

Microstructure of Al-2%Si and Al-6%Si Strips Cast Using Vertical-Type High-Speed Twin-Roll Caster

Al-2%Si and Al-6%Si were cast at a roll speed of 30 m/min and a roll load of 5 N/mm using a vertical-type high-speed twin-roll caster. The rolls were suddenly stopped during casting and the molten metal was solidified. The effect of Si content on the microstructure at the cross section near the roll bite was investigated using Weck’s reagent. The cross section of the Al-2%Si strip consisted of five layers (one center layer, two middle layers, and two surface layers) at the roll bite and that of the Al-6%Si strip consisted of three layers (one center layer and two side layers). The a-Al in the center layer was globular for both Al-2%Si and Al-6%Si. The relative thickness of the center layer for Al-6%Si was greater than that for Al-2%Si. In Al-2%Si, the surface layer had a very fine chill-zone microstructure. The Si solid-solution content in the α-Al in the surface layers and the center layer was less than that in the middle layers in the Al-2%Si strip.

Influence of Si content on thermoelectric properties of Mg2(Sn,Si) films by sputtering

Mg2(Sn,Si) films with different Si content were prepared by magnetron sputtering. The phase composition, surface and cross-sectional morphology, chemical composition and element distribution, carrier concentration, carrier mobility, electrical conductivity, Seebeck coefficient and power factor of the deposited Mg–Sn–Si films were studied. The results show that the deposited films are composed of Mg2(Sn,Si) solid solution phase and a small amount of metal Mg phase. The room temperature carrier concentration decreases and mobility increases with increasing Si content in deposited Mg–Sn–Si films, respectively. The room temperature electrical conductivity and Seebeck coefficient decreases and increases with increasing Si content, respectively. The deposited Mg2(Sn,Si) films with moderate Si content possess the maximum power factor value of 2.76 mW m−1 K−2 at 303 °C and its room temperature figure of merit reaches the highest value of 0.44. The thermal conductivity decreases with increasing Si content, indicating that the lattice distortion caused by Si doping can reduce the thermal conductivity of the deposited films.

Efficient prediction of corrosion behavior in ternary Ni-based alloy systems: Theoretical calculations and experimental verification

Pourbaix diagrams are calculated to describe electrochemical processes for alloys in aqueous solution. With the multi-component differentiation of alloy systems, the construction of Pourbaix diagrams is facing challenges, especially for non-single-phase alloy systems. In this study, the simultaneous construction of phase diagrams and Pourbaix diagrams were implemented for predicting the evolution of the phases in the immune and passive regions. The CALPHAD (CALculation of PHAse Diagram) approach was used to quickly access the Gibbs free energies of various phases and the chemical potential of the elements in the phases from the thermodynamic database of the Ni-Si-Al-Y system. The corrosion behavior of two typical Ni-Al-Si and Ni-Al-Y systems was investigated. Si and Y were added to Ni-based alloys to produce the solid solutions L12Ni3(Al,Si) and L12Ni3Al + Ni5Y, respectively. Calculations showed that NiO and Al2O3 make up the passive area of the Ni3Al1 alloy. The introduction of SiO2 and Y(OH)3 in the passive region separately helped to minimize the alloys' susceptibility to corrosion. However, Si reduced the thermodynamical possibility of NiO formation in the passive film, and the addition of Y caused extreme galvanic corrosion. Experiments on Ni-based alloys validated the results through electrochemical corrosion. It was also discovered that the presence of Ni5Y produced galvanic corrosion and that Si reduced the oxide in the passive film, causing pitting corrosion. The corrosion prediction of the quaternary alloys indicates that the solid solution of Si in Ni5Y reduces the galvanic corrosion effect and the dissolution of passive film. The current work demonstrates that phase diagrams and Pourbaix diagrams may be efficiently and accurately predicted using a well-constructed thermodynamic database, which has major implications for future studies on the corrosion behavior of multi-component alloys.

Characterization of MoAlB ceramics synthesized via spark plasma sintering with Si addition and SiC reinforcement

The MoAlB phase with high purity and density from elemental precursors was successfully synthesized with SPS (Spark Plasma Sintering) at 1200 °C. Then, MoAlB-Si solid solution and MoAlB-SiC (5% SiC by volume) composite were fabricated to improve the mechanical properties and oxidation behavior of the MoAlB further. XRD (X-Ray Diffraction), SEM (Scanning Electron Microscopy), and EDS (Energy Dispersive X-Ray Spectroscopy) investigated the composition and microstructure of the MoAlB ceramics. The hardness was measured by the Vickers indentation test, and fracture toughness was calculated by radial cracks formed during the indentation test. The hardness and fracture toughness of pure MoAlB was 10.30 GPa and 6.73 MPa.m1/2. With the Si solid solution, the hardness increased to 11.93 GPa, while the fracture toughness decreased to 5.49 MPa.m1/2. The highest hardness and fracture toughness were obtained in the MoAlB-SiC composite, 12.39 GPa, and 7.38 MPa.m1/2, respectively. The oxidation tests of the samples were characterized in the air at 1200 ℃ for 12 h. A dense and continuous oxide layer was formed in all samples after 12 h at 1200 °C. While both Si solid solution and SiC reinforcement increase the oxidation resistance, the best results were obtained in the MoAlB-Si-SiC composite. The effect of Si addition and SiC reinforcement on electrical and thermal conductivity was measured from room temperature to 1000 ⁰C. The electrical conductivity of all samples decreased exponentially with the increase in temperature. The electrical conductivity of pure MoAlB was 2.82 S⋅m−1 at room temperature and decreased with the Si addition (2.49 S⋅m−1) or SiC reinforcement (2.67 S⋅m−1). On the other hand, thermal conductivity tends to decrease between room temperature to 400 °C but showed an increasing trend above 400 °C. In conclusion, the mechanical properties and oxidation resistance of MoAlB ceramics were improved with Si addition and SiC reinforcement.

Formation mechanism and effect on the mechanical properties of TiSi phase for Ti-5Al-5Mo-5Cr-3Nb-2Zr alloyed by silicon

To investigate the formation mechanism and evaluate the silicide effect on the microstructure and mechanical properties of Ti–5Al–5Mo–5Cr–3 Nb–2Zr–xSi (Ti–xSi, wt%, x = 0, 0.2, 0.4, 0.6, 0.8) alloys, they are melted via vacuum arc melting and observed by scanning electron microscope (SEM) and transmission electron microscopy (TEM). The results indicate that their microstructure comprises grain boundary α (αGB), secondary α (αs), primary α (αp), and residual β phases when the Si content is less than 0.2 wt%. With an increase in the Si content from 0.4 to 0.8 wt%, the content of the TiSi phase precipitated in αGB phase increases. Moreover, its size increases from 40 nm to 0.8 µm. The diffusion of Si atoms from their high concentration in the β to the α phase of the supersaturated solid solution is hindered by the phase boundary, resulting in the precipitation of silicides. The high energy at the interface and the diffusion of Si accelerate this precipitation. The elongation and fracture toughness increase at 0–0.2 wt% Si and then decrease at 0.4–0.8 wt% Si, peaking at Ti–0.2Si (7.1% and 66.4 MPa·m1/2, respectively). The strength is improved owing to the Si solid solution strengthening, precipitation of Ti5Si3 and TiSi phases, and strengthening effect caused by the difference in crystal plane spacing between the TiSi and the αGB phases. A higher silicide content leads to a gradual transformation from an intergranular ductile fracture to intergranular brittle fracture.

Microstructure evolution, mechanical properties and fracture behavior of Al-xSi/AZ91D bimetallic composites prepared by a compound casting

In this paper, the effect of the Si content on microstructure evolution, mechanical properties, and fracture behavior of the Al-xSi/AZ91D bimetallic composites prepared by compound casting was investigated systematically. The obtained results showed that all the Al-xSi/AZ91D bimetallic composites had a metallurgical reaction layer (MRL), whose thickness increased with increasing Si content for the hypoeutectic Al-Si/AZ91D composites, while the hypereutectic Al-Si/AZ91D composites were opposite. The MRL included eutectic layer (E layer), intermetallic compound layer (IMC layer) and transition region layer (T layer). In the IMC layer, the hypereutectic Al-Si/AZ91D composites contained some Si solid solution and flocculent Mg2Si+Al-Mg IMCs phases not presented in the hypoeutectic Al-Si/AZ91D composites. Besides, increasing Si content, the thickness proportion of the T layer increased, forming an inconsistent preferred orientation of the MRL. The shear strengths of the Al-xSi/AZ91D bimetallic composites enhanced with increasing Si content, and the Al-15Si/AZ91D composite obtained a maximum shear strength of 58.6 MPa, which was 73.4% higher than the Al-6Si/AZ91D composite. The fractures of the Al-xSi/AZ91D bimetallic composites transformed from the T layer into the E layer with the increase of the Si content. The improvement of the shear strength of the Al-xSi/AZ91D bimetallic composites was attributed to the synergistic action of the Mg2Si particle reinforcement, the reduction of oxidizing inclusions and the ratio of Al-Mg IMCs as well as the orientation change of the MRL.

High entropy steel processed through mechanical alloying and spark plasma sintering: Alloying behaviour, thermal stability and mechanical properties

In present investigation, a non-equiatomic high entropy steel (HES) was synthesized by mechanical alloying (MA) followed by spark plasma sintering (SPS). The Fe40Mn14Ni10Ti10Al15Si10–C1 HES milled up to 30 h was found to have a metastable dual-phase containing a major BCC (a = 2.872 Å; cI2) and a γ-brass type (a = 8.890 Å; cI52) phase having nanostructured grains of ∼10 ± 2 nm. The differential scanning calorimetry (DSC) thermogram exhibited the four exothermic heating events at 530 °C, 690 °C, 860 °C and 1000 °C. The phase transformation corresponding to the heating events was correlated with the ex-situ XRD of the as-milled powder. The phases evolved were Fe–Si solid solution, FCC, Fe5Si3 type and TiC phases. Fe40Mn14Ni10Ti10Al15Si10–C1 milled HES powder was consolidated through SPS at 900 °C and at 50 MPa. The SPSed HES were found to have a dual-phase structure containing a major FCC phase (a = 3.602 Å; cF4) and a minor BCC phase (a = 2.876 Å; cI2) along with the intermetallic phases like Fe5Si3 type (a = b = 6.808 Å, c = 4.745 Å; hP16) and TiC (a = 4.301 Å; cF8). The mechanical properties of these SPSed samples were discerned through instrumented microhardness and compression tests. The microhardness, elastic modulus, ultimate compressive strength and strain were found to be ∼10.4 GPa, ∼209 GPa, ∼2305 MPa and ∼15% respectively. This SPSed HES showed an excellent room temperature microhardness and strength which can be attributed to the co-existence of FCC phase along with the minor phases and hard intermetallics. The strengthening mechanism suggested that the grain boundary, dislocation, and precipitates strengthening were dominant. Attempts have been made to understand the phase evolution and the consequent mechanical properties in these HES.

Extraordinary Antiwear Properties of Graphene-Reinforced Ti Composites Induced by Interfacial Decoration.

The expected excellent lubricant effect of graphene in metals during friction and wear is rarely achieved because of the difficulty in synthesizing suitable interfaces. Particularly, the situation is more challenging in titanium (Ti) matrix composites (TMCs) because of the high chemical-interface-reaction tendency between graphene and Ti during composite fabrication. In this study, few-layered graphene (FLG) decorated with SiC nanoparticles (SiCp) was synthesized as reinforcement in Ti-6Al-4V alloy to improve the interface of the composites. It was found that interfacial SiCp not only strengthened the interface bonding by the Si solid solution but also inhibited the chemical reaction between FLG and the Ti matrix with reduced sp3 defects. The composite with 30 wt % SiC-decorated FLG showed an 86.8% decrement in wear rate compared to the unreinforced matrix, resulting in exceptionally high antiwear enhancing efficiency, which was around fourfold of the available values of other TMCs in the literature. The antiwear mechanism was investigated by thorough characterization of the interfaces and microstructures of the composites. The idea of interfacial decoration can be potentially applied to other nanocarbon/metal composites with the advantages of retaining the function performance of nanocarbon materials.

Ultrafine-grained microstructure and controllable magnetic domains in Fe-based nanocrystalline alloys with excellent magnetic properties induced by hot isostatic pressing

The coarsening and inhomogeneous distribution of nano-grains caused by traditional heat treatment processes are the biggest obstacles for obtaining ultrahigh permeability and excellent comprehensive soft magnetic properties in Fe-based nanocrystalline alloys. Here, we propose a new strategy to control grain growth and magnetic anisotropy, by introducing isotropic compressive stress field in the annealing process to optimize the magnetic properties. Compared with conventional isothermal annealing, the coupling of stress-temperature field generated by hot isostatic pressing (HIP) induced the microstructure, magnetic domain evolution and magnetic properties in Si-rich Fe73.5Si15.5B7Nb3Cu1 amorphous ribbons have been systematically investigated. We demonstrate that HIP treatment promotes more Si atoms to dissolve in Fe unit cell to form Fe(Si) solid solution causing an increase in interplanar spacing. Also, the high-density Cu clusters precipitate in the amorphous matrix upon HIP serving as nucleation sites for α-Fe(Si) grains, which facilitate a high volume fraction, uniform and ultrafine-grained microstructure. Moreover, the existence of stress field introduces induced anisotropy effectively controls the magnetization mechanism and magnetic structure evolution. Furthermore, the Fe73.5Si15.5B7Nb3Cu1 nanocrystalline alloy treated by HIP exhibit excellent comprehensive magnetic properties, such as high Ms, high μe, low Pcv, low AC Hc and high Br/Bm.

Improvement in the Resistance to Wear of Work-Rolls Used in Finishing Stands of the Hot Strip Mills

Work-rolls manufactured through the Indefinite Chill Double Poured (ICDP) method present an exterior work layer manufactured in a martensitic white cast iron alloyed with 4.5 %Ni, 1.7 %Cr, and 0.7 %Nb (wt.%). In its microstructure, there are abundant carbides of the type M3C and MC, which give high resistance to wear, and graphite particles which improve the service behaviour of the rolls against thermal cycling. The core of the rolls is manufactured in grey cast iron of pearlitic matrix and spheroidal graphite. These work-rolls are used in the finishing stands in Hot Strip Mills for rolling slabs proceeding from continuous casting at 1200 °C. Through the application of a Design of Experiments (DoE), an attempt has been made to identify those manufacturing factors which have a significant effect on resistance to wear of these rolls and to find an optimal combination of levels of these factors which allow for improvement in resistance to wear. To increase resistance to wear, it is recommended to situate, simultaneously, the liquidus temperature and the percentage of Si in the respective ranges of 1250–1255 °C and 1.1–1.15 (wt.%). Higher liquidus temperatures favour the presence of the pro-eutectic constituent rather than the eutectic constituent. The outer zone of the work layer, in contact with the metal sheet, which is being rolled, does not show the graphitising effect of Si (0.8–1.15 wt.%). On the contrary, it confirms the hardening effect of the Si in solid solution of the ferrite. The addition of 0.02% of Mg (wt.%) and the inoculation of 6 kg/T of FeB tend to eliminate the graphitising effect of the Si, thus favouring that the undissolved carbon in the austenite is found to form carbides in contrast to the majority formation of graphite.

Hexagonal Si-Ge Class of Semiconducting Alloys Prepared by Using Pressure and Temperature.

Multi-anvil and laser-heated diamond anvil methods have been used to subject Ge and Si mixtures to pressures and temperatures of between 12 and 17 GPa and 1500-1800 K, respectively. Synchrotron angle dispersive X-ray diffraction, precession electron diffraction and chemical analysis using electron microscopy, reveal recovery at ambient pressure of hexagonal Ge-Si solid solutions (P63 /mmc). Taken together, the multi-anvil and diamond anvil results reveal that hexagonal solid solutions can be prepared for all Ge-Si compositions. This hexagonal class of solid solutions constitutes a significant expansion of the bulk Ge-Si solid solution family, and is of interest for optoelectronic applications.

Solute-induced strengthening during creep of an aged-hardened Al-Mn-Zr alloy

We examine the precipitation and creep behavior of Al-0.5Mn-0.02Si (at.%) alloys, with and without the L12-forming elements Zr and Er (0.09 and 0.05 at.%, respectively), utilizing isochronal aging experiments as well as compressive and tensile creep tests performed between 275 and 400 °C. The Al-0.5Mn-0.09Zr-0.05Er-0.05Si alloy exhibits an unusually high creep resistance in the peak-aged state, which is significantly better than that observed generally in its Mn-free L12-strengthened counterparts; for example, the creep threshold stresses at 300 °C are 34-37 MPa, about three times higher than those in a Mn-free Al-0.11Zr-0.005Er-0.02Si alloy. Scanning transmission electron microscopy illustrates that nanoscale Al3(Zr,Er) L12-precipitates are formed in the dendritic cores and micron-sized Al(Mn,Fe)Si α-precipitates in the interdendritic channels. Moreover, the Al(f.c.c.)-matrix remains supersaturated with randomly distributed Mn solute atoms, as determined by atom-probe tomography and electrical conductivity measurements, for months at creep temperatures. Creep experiments on the Zr- and Er-free Al-0.5Mn-0.02Si solid-solution alloy reveal a small primary creep strain, a high apparent stress exponent, na ∼9-7, and a threshold-stress-type behavior. After ruling out other possible mechanisms, we provide evidence that the threshold stress in this precipitate-free alloy originates from dislocation/solute elastic interactions leading to a strong drag force exerted on edge dislocations, hindering their ability to climb. The relatively high creep resistance of Al-0.5Mn-0.09Zr-0.05Er-0.05Si is interpreted in terms of the synergy between this solute-induced threshold stress (SITS, from Mn in solid-solution) and the known precipitate-bypass threshold stress (from the L12-nanoprecipitates).

Microstructure evolution and reaction behavior of Cu–Ni–Si powder system under solid-state sintering

Cu–Ni–Si powder compacts were firstly prepared by mechanical mixing and cold-pressing, and then held at 600, 700, 800, 900, 950 and 1000 °C for 5 min followed by water-quenching. Subsequently, X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and transmission electron microscope (TEM) were used to characterize the microstructure and phase composition of water-quenched samples, and competitive reactions among Ni–Si compounds were also discussed. Finally, a schematic diagram about the solid-state reaction process of Cu–Ni–Si powder system was proposed. Results showed that Ni and Si substances started to diffuse and reacted when the temperature was above 600 °C, resulting in the formations of Ni31Si12 phase at the primary powder boundary and Ni2Si precipitations inside the Cu powder, respectively. With the increase of temperature, Ni2Si phase dissolved into Cu matrix while the amount and size of Ni31Si12 phase increased along with the morphology changing from chrysanthemum-like shape to equiaxed structure. The final microstructure of Cu–Ni–Si powder system after sintering and water quenching consisted of Cu(Ni,Si) solid solution and equiaxed Ni31Si12 phase at the primary powder boundary, which was expected to achieve a combination of high strength and high electrical conductivity by subsequent heat treatments.

A simultaneous improvement of the strength and plasticity of spring steels by replacing Mo with Si

A synchronous improvement of the strength and plasticity (SISP) is a significantly important subject attracted by many researchers. In this study, the key factors affecting the plasticity and strength of spring steels were analyzed and discussed in detail. Meanwhile, the differences in the microstructures and fractographies between two Cr–Mn steels were compared. It is found that the 50CrMnSiVNb spring steel has higher strength as a result of the dislocation strengthening, the solution strengthening caused by the Si solid solution as well as higher work-hardening capacity by comparing four strengthening mechanisms and work-hardening capacity. Furthermore, the better plasticity of the 50CrMnSiVNb steel may be mainly attributed to the lighter banded segregation and hydrogen embrittlement compared with the 50CrMnMoVNb steel. This study may enrich the fundamental knowledge regarding how to optimize the composition of spring steel and provide some new ideas for synchronous improvement of the strength and plasticity of spring steels.