•Deformation behavior of hard metal material was demonstrated on the atomic scale.•The plasticity origin was analyzed for WC, Co and WC-Co composite.•The semi-coherent interface contributes to plastic coordination through stress transmission.The deformation characteristics and plasticity mechanisms of the WC-Co composite were demonstrated by the molecular dynamics simulations on the atomic scale. It was found that the nucleation, expansion and interaction of dislocations are distinctly dependent on the orientation where the load is applied. At the same indentation depth, the dislocation density in WC is lower by an order of magnitude than in Co. When the indentation is applied on the WC basal plane, the dislocations form firstly on the pyramidal planes and are inclined to slip on the prismatic planes. At the incoherent WC/Co interface in the WC-Co composite, the distortion occurs with loading. In contrast, at the semi-coherent WC/Co interface containing dislocation network, the stress concentration is coordinated, and the nucleation of dislocations in Co is triggered. This is favorable to enhance the resistance against intergranular fracture of the WC-Co composite.The plasticity characteristics and mechanisms of the hard metal material were studied for the components of WC, Co and WC-Co composite. The WC/Co semi-coherent interface contributes to coordinate stress concentration and facilitates the start-up of dislocations in Co, which is favorable to enhance the resistance against intergranular fracture of the WC-Co composite.Download high-res image (302KB)Download full-size image

•Fe, Ni and Nb doped nanocrystalline Sm5Co19 based alloys were for the first time prepared.•Doping leads to formation of highly dispersed 5:19H nanoprecipitates in the 5:19 R matrix.•Ni doping increases both the coercivity and saturated magnization at high temperatures.The nanocrystalline Sm5Co19 based alloys were firstly prepared, with Fe, Ni and Nb as doping elements. The microstructure, crystal structure and magnetic properties at room temperature and high temperatures were studied for the nanocrystalline alloys, and the effects of doping elements on the microstructure and magnetic performance were analyzed. It was found that Ni, Fe and Nb doping facilitated transformation from rhombohedral to hexagonal structure of the nanocrystalline Sm5Co19 based alloys. The nanoparticles with the hexagonal structure enhance the coercivity of the nanocrystalline alloys. At high temperatures, as compared with the binary Sm5Co19 alloys, the dispersed nanoparticles containing Fe and Ni increase both the coercivity and saturated magnization, from which good high-temperature magnetic performance of the nanocrystalline Sm5Co19 based alloys were obtained. The results may facilitate development of new type Sm-Co alloys with high magnetocrystalline anisotropy and good high-temperature magnetic performance.

A hybrid model that combines first principles calculations and thermodynamic evaluation was developed to describe the thermal stability of a nanocrystalline solid solution with weak segregation. The dependence of the solute segregation behavior on the electronic structure, solute concentration, grain size and temperature was demonstrated, using the nanocrystalline Cu–Zn system as an example. The modeling results show that the segregation energy changes with the solute concentration in a form of nonmonotonic function. The change in the total Gibbs free energy indicates that at a constant solute concentration and a given temperature, a nanocrystalline structure can remain stable when the initial grain size is controlled in a critical range. In experiments, dense nanocrystalline Cu–Zn alloy bulk was prepared, and a series of annealing experiments were performed to examine the thermal stability of the nanograins. The experimental measurements confirmed the model predictions that with a certain solute concentration, a state of steady nanograin growth can be achieved at high temperatures when the initial grain size is controlled in a critical range. The present work proposes that in weak solute segregation systems, the nanograin structure can be kept thermally stable by adjusting the solute concentration and initial grain size.

•Microstructural design of the bimodal-grained WC-Co feedstock powder•Remarkable increase in wear resistance of the fabricated coating•Understanding of the effects of nanoscale and coarse WC on properties of coatingA new type of bimodal-grained WC-Co cemented carbide coating was fabricated, using the raw materials consisting of the in situ synthesized nanoscale WC-Co composite powder as major component and a certain amount of ultra-coarse WC particles as addition. The effects of coarse WC particles on the microstructure, mechanical properties and wear behaviour of the coating were investigated. It was found that with a suitable addition of coarse WC particles, the coating has a decreased decarburization and significantly increased wear resistance, as compared with the coating without the addition. The coarse WC particles allow a certain degree of plastic deformation by dislocation gliding so that under wearing conditions some stress concentration can be released and their fractures are inhibited. A good combination of coarse WC particles and WC-Co nanocomposite facilitates high properties of the coating, with the former mainly bearing the load and resisting against penetration of the wear debris, and the latter providing high hardness and also plastic accommodation in the wearing process.

WC–Co cemented carbide bulk materials with anisotropic distribution of specific WC planes were prepared by spark plasma sintering (SPS) using different pre-sintering temperatures of 850 °C, 900 °C and 1000 °C at a constant pressure of 60 MPa. The coincidence site lattice (CSL) grain boundaries were characterized and the anisotropic distribution of the CSL boundaries was demonstrated. The combined effects of the composite powder and the SPS parameters on the formation of the anisotropic CSL boundary distribution were analyzed. The mechanisms were proposed such that the CSL grain boundary distribution can be tailored by adjusting the composition of the composite powder and the SPS processing parameters such as the pre-sintering temperature, sintering pressure and its working stage. The findings facilitate to obtain a beneficial CSL grain boundary distribution that enhances mechanical properties in certain directions of the cemented carbide.

The real-time charge and discharge processes of a single phase nanocrystalline Li2C2 alloy were directly observed by in situ transmission electron microscopy. Upon lithiation, nanocrystalline Li2C2 exhibits obvious volume expansion and morphology change, and an amorphous structure is generated from the nanocrystalline matrix. The change of structure affects the cycling stability of nanocrystalline Li2C2 as a cathode material. To reduce the effect of the structural change, the degree of delithiation was optimized by controlling the charge/discharge voltage range in the electrochemical tests. A high initial specific capacity of 352 mA h g−1 was obtained for nanocrystalline Li2C2, and a discharge capacity of 171 mA h g−1 was maintained after 50 cycles. The present work proposed a new alloy-type cathode material of nanocrystalline Li2C2 for lithium ion batteries with promising electrochemical performance.

The effects of Hf doping on the phase constitution and its evolution of the SmCo7−xHfx (0 ≤ x ≤ 0.5) nanocrystalline alloys were investigated. It was found that a single TbCu7-type metastable phase can be stabilized in the nanocrystalline SmCo7−xHfx alloys with x ≤ 0.25, and the phase decomposition occurs at higher Hf doping contents. The Hf doping plays a significant role in inhibiting grain growth at high temperatures, which is favorable for the high-temperature magnetic properties. The metastable phase is stabilized by the combined effects of nanostructuring and Hf doping. Moreover, the magnetic performance is increased due to the pinning effect and the high magnetocrystalline anisotropy of the stabilized TbCu7-type phase.

A novel fabrication method combining in situ reactions and reactive sintering to prepare WC-Co cemented carbides with highly oriented WC grains and specific mechanical properties was developed. Low synthesis temperature and short holding time were used to synthesize WC-Co based composite powder through in situ reduction and carbonization reactions, and the subsequent consolidation was performed in the spark plasma sintering system. The microstructure of the resultant cemented carbide bulk material has obviously higher fraction of the WC basal planes on the cross-section which is perpendicular to the pressing direction of the sintering powder, the area percentage reaches 5 times of that on the cross-section parallel to the pressure direction. Correspondingly, the hardness, elastic modulus and wear resistance measured on the cross-section perpendicular to the pressing direction are simultaneously increased greatly with highly oriented WC grains in the microstructure.

Sm–Co alloys with the stabilized SmCo7 phase are most prominent candidates for advanced high temperature permanent magnets, where the stabilization of the SmCo7 phase can be effectuated by nanostructuring. The complex concurrent processes of ordering and phase transformation in a SmCo7 nanograin are characterized on the atomic scale. For the first time early stages of the phase transformation are made visible by highlighting specific superstructures in single nanograins using Fourier reconstruction of high-resolution transmission electron microscopy images. The superstructures are only detectable and can only be distinguished in specific crystallographic orientations. The evolution of the atom arrangement in the crystal structures is demonstrated for the concurrent ordering process and phase transformation. During decomposition of the metastable SmCo7 phase, the hexagonal Sm2Co17 superstructure (2:17H) forms at first as a precursor of the rhombohedral Sm2Co17 superstructure (2:17R) – this can only be detected by analysis of individual grains and has not been described so far. By extensive crystallographic analysis of individual nanograins, a distinct correlation between the fraction of the superstructure phases and the grain size is found, showing directly and unambiguously the grain size dependence of the phase transformation in the nanocrystalline alloy, a phenomenon that so far has only been shown indirectly using volume averaging methods.

The carbon content was adjusted in the raw materials used to synthesize the WC-Co composite powder by in situ reactions. It was found that in the sintered nanocrystalline cemented carbide bulk, the matching of key planes (0001), (10−10) and (10−11) was influenced by the carbon content. The matching relationship plays an important role in the mechanical properties of the bulk material along certain directions. At an optimized carbon content of 16.09 wt% for the WC-6Co cemented carbide, both high hardness (2130 kg mm−2) and high toughness (11.8 MPa m1/2) were achieved simultaneously.

A thermodynamic model was developed in particular for nanocrystalline partially ionic solids, which represent a group of Li ion battery anode materials. The lithium compounds were used as examples to demonstrate the model applications in studies of phase stability and phase transformation behavior in the nanoscale anode system. The peritectic and eutectic transformations were described systematically concerning the reaction temperatures and liquid concentrations at various equilibria, in which the grain size effects on the equilibrium, stability and transformation of Li-containing phases were quantified. To verify the model predictions, a series of experiments were performed using the nanocrystalline Li–Si system as sample materials. The experimental finding confirmed the model calculations, based on which the correlation of phase stability, temperature, grain size and critical grain size was proposed.

The negative thermal expansion (NTE) properties of the antiperovskite manganese nitrides with micron-scale, submicron-scale and nanometer-scale microstructures, respectively, were investigated using the Mn3Cu0.5Ge0.5N composition as an example. It was discovered that the NTE start temperature, NTE operation temperature range and coefficient of NTE change obviously in a wide range with decreasing the grain size level of the microstructure. The mechanisms for the broadening of the NTE operation temperature range and the decrease in the absolute value of NTE coefficient were proposed based on the grain-size-dependence of the frustrated magnetic interactions and magnetic ordering. The present study indicates that the NTE properties of the antiperovskite manganese nitrides can be tailored by the control of the microstructure scale.

The inherently high magnetic anisotropy and nanoscale grain size in a Sm5Co19 compound result in an intrinsic coercivity far higher than those of known Sm–Co compounds prior to orientation treatment. The combination of ultrahigh intrinsic coercivity, high Curie temperature and low coercivity temperature coefficient of nanocrystalline Sm5Co19 as a single phase material shows it to be a very promising compound to develop outstanding high-temperature permanent magnets.

Ultrafine WC–Co materials were prepared by a developed route combining in-situ synthesis of composite powder and sinter-HIP technique. Simultaneous enhancement in fracture toughness and transverse rupture strength has been achieved in the prepared cemented carbide. Based on detailed characterizations of Co binder phase, dislocations in WC grains and interfacial features, the mechanisms for co-enhancement in fracture toughness and strength of cemented carbides are proposed.

•Controllable carbon content in prepared composite powder and spraying feedstock.•Excellent mechanical properties of the ultrafine-structured WC–Co coating.•Mechanisms for estimation of the toughness of cermet coatings.The ultrafine WC–Co composite powder was synthesized by in situ reactions of metal oxides and carbon. The thermal spraying feedstock was prepared by granulation using the as-synthesized composite powder. The influence of carbon addition in the starting powders on the phase constitution and chemical composition of the prepared composite powder and spraying feedstock as well as on the microstructure and mechanical properties of the sprayed cermet coating was investigated. By adjusting the carbon addition in the initial stage, the pure phase constitution can be obtained in the prepared spraying feedstock. In the subsequent thermal spraying, the decarburization can be inhibited by the free carbon existing in the feedstock powder. With an appropriate carbon addition, the prepared ultrafine-structured coating has the best combination of hardness and toughness and thus the coating exhibits the highest wear resistance. The present work indicates the significant role of carbon control during the preparation processes of WC–Co coatings.By adjusting the carbon addition in the initial stage, the decarburization of coating can be inhibited. The prepared ultrafine-structured WC–Co coating has the best combination of hardness and toughness, leading to the high wear resistance.

Single-phase ultrafine nanocrystalline Li2C2 alloy was prepared using a simple and efficient technique that combines the ball milling process and spark plasma sintering. The crystal structure of the nanocrystalline Li2C2 alloy was constructed by the Rietveld refinement based on the X-ray diffraction pattern of the prepared nanocrystalline sample. Furthermore, the phase stability in the nanocrystalline Li2C2 alloy was quantitatively studied using the developed thermodynamic model for the nanocrystalline alloys. It has been found that in a certain low temperature range, the β-Li2C2, which is a metastable phase in the coarse-grained polycrystalline system, can be stabilized due to the nanograin size effect.Highlights► A route is developed to prepare pure and single-phase nanocrystalline Li2C2 alloy bulk. ► Details of crystal structure of nanocrystalline Li2C2 are shown. ► Phase stability in nanocrystalline Li2C2 alloy is quantitatively described.

The ultrafine WC–Co composite powder was synthesized by a newly developed rapid route based on in situ reactions. By using the as-synthesized composite powder, the granulation processing was then carried out to prepare the ultrafine-structured thermal spraying feedstock. The influences of the heat-treatment process on density of the feedstock powder, phase constitution and wear resistance of the resultant WC–Co coatings fabricated by high velocity oxy-fuel (HVOF) were investigated. The results showed that increasing the heating temperature and extending the holding time leaded to remarkable increase in the density and flowability of the feedstock powder. As a result, the decarburization of the in-flight particles could be decreased and the wear resistance of coating was significantly enhanced. The present study demonstrated that the developed techniques for the ultrafine powder and its thermal-sprayed coatings had very promising applications in scaling up to produce ultrafine-structured cermet coatings with excellent performance.

The present study was focused on the subsequent heat-treatment of the in-situ synthesized WC–Co composite powder and its effect on the properties of the cemented carbides prepared by sinter-HIP. The element composition, phase constitution, microstructure characteristics and properties of the prepared cemented carbides were analyzed quantitatively. The heat-treatment of the composite powder before sintering plays a significant role in the characteristics of the microstructure and properties of the WC–Co bulk material. The optimized heat-treatment parameters for the composite powder were obtained, from which the excellent combination mechanical properties were achieved for the sintered WC–Co bulk material.

•Low-Co Sm–Co alloy as new candidate for permanent magnets was proposed.•Relationship between the phase stability and grain size was quantified for Sm2Co7.•The work contributes to the development of nanostructured Sm–Co permanent magnetic materials.In contrast to the conventional polycrystalline low-Co Sm–Co alloys that have very weak permanent magnetic properties, the Sm2Co7 alloy has been found to have fairly promising permanent magnetic performance when its grain size is reduced to the nanoscale. It was discovered that the crystal structure of the nanocrystalline Sm2Co7 has a strong nanograin-size-dependent stability. The rhombohedral structure of Sm2Co7 phase which is metastable at temperatures lower than 1435 K in conventional polycrystalline system can exist stably at room temperature in the nanocrystalline system. To understand the phase stability of the nanocrystalline Sm2Co7, the experimental and nanothermodynamic analyses were combined to describe quantitatively the phase transformation behavior of Sm2Co7 on the nanoscale. The results are important for the development of nanostructured Sm–Co permanent magnets.

Based on a unique method to synthesize WC–Co composite powder by in-situ reactions of metal oxides and carbon, the effects of the carbon addition in the initial powders on the phase constitution, microstructure and mechanical properties of the cemented carbides were investigated. It is found that with a suitable carbon addition the pure phase constitution can be obtained in the sintered bulk from the composite powder. The mechanical properties of the cemented carbides depend on the phase constitution and the WC grain structure. To obtain the excellent properties of the WC–Co bulk, it is important to obtain the pure phase constitution from the appropriate carbon addition in the initial powders and a suitable grain size.

The spark plasma sintering (SPS) and hot isostatic pressing (sinter-HIP) were taken as the representative methods of rapid sintering and liquid-state sintering technologies, respectively, to fabricate the WC–Co cemented carbides. The microstructures and properties of the bulk materials prepared by the two techniques were characterized and compared systematically. It was demonstrated that the big difference in mechanical properties of the cemented carbides prepared by SPS and sinter-HIP depends on the configuration of WC and Co phases and the WC/Co orientation relationship, which result from the intrinsic features of the sintering technologies. The mechanisms for the excellent properties obtained in the cemented carbides prepared by sinter-HIP were proposed, based on which the favorable microstructures and optimized processing methods concerning liquid-state sintering may be developed.Highlights► Representative methods of rapid sintering and liquid-state sintering. ► Big difference in mechanical properties of two kinds of samples. ► Mechanism related to configuration and orientation relationship of WC and Co phases. ► Intrinsic features of sintering technologies and their effects.

In the present study, a complete route which integrates in-situ synthesis of WC–Co composite powder and sinter-HIP is proposed to prepare the ultrafine tungsten carbides. Owing to the in-situ reduction and carbonization reactions of WO2.9, Co3O4 and carbon black powders at 1000 °C, the composite powder with pure phase constitution and ultrafine particle size is synthesized with a rapid procedure. The WC–Co bulk material prepared by the sinter-HIP densification of the composite powder exhibits homogeneous and ultrafine microstructure, as well as the excellent mechanical properties. The proposed method shows potential to be developed as a promising industrial route owing to its advantages of low-cost raw materials and short-term in-situ reactions.

The characteristics of phase transformation in nanocrystalline alloys were studied both theoretically and experimentally from the viewpoint of thermodynamics. With a developed thermodynamic model, the dependence of phase stability and phase transformation tendency on the temperature and the nanograin size were calculated for the nanocrystalline Sm2Co17 alloy. It is thermodynamically predicted that the critical grain size for the phase transformation between hexagonal and rhombohedral nanocrystalline Sm2Co17 phases increases with increasing temperature. When the grain size is reduced to below 30 nm, the hexagonal Sm2Co17 phase can stay stable at room temperature, which is a stable phase only at temperatures above 1520 K in the conventional polycrystalline alloys. A series of experiments were performed to investigate the correlation between the phase constitution and the grain structure in the nanocrystalline Sm2Co17 alloy with different grain size levels. The experimental results agree well with the thermodynamic predictions of the grain-size dependence of the room-temperature phase stability. It is proposed that at a given temperature the thermodynamic properties, as well as the phase stability and phase transformation behavior of the nanocrystalline alloys, are modulated by the variation of nanograin size, i.e. the grain size effects on the structure and energy state of the nanograin boundaries.

The ultrafine-grained ζ-Mn2N0.86 compound bulk was prepared by a novel method that combined the solid-gas reaction, ball milling and spark plasma sintering. Characterizations on the magnetic properties showed that the Néel temperatures of the ball-milled powder and the ultrafine-grained bulk of Mn2N0.86 compound are drastically reduced as compared with the coarse-grained polycrystalline ζ-phase Mn-N compounds. Furthermore, it was found that the antiferromagnetism and the weak ferromagnetism coexist in the ball-milled powder and the ultrafine-grained bulk of Mn2N0.86 compound.

The nanoparticles and nanocrystalline bulk of pure gadolinium (Gd) were prepared by a novel route. The nanostructures of the single particle and the bulk of Gd were investigated, and the crystal structure was characterized. The fundamental properties, namely the physical, thermal, and mechanical characteristics, were studied for the prepared Gd bulk with an ultrafine nanograin structure. As compared with the conventional polycrystalline metal, the ultrafine nanocrystalline Gd has greatly enhanced functional and structural properties. The physical background for the changes of the fundamental properties with the reduction of the grain size to the nanoscale was analyzed.

Ultrafine-grained WC-Co bulk materials were prepared by a new method that contains pretreatment of the milled powder mixture and subsequent spark plasma sintering (SPS). Ball milling parameters and the pretreatment temperature have significant effects on the microstructure and properties of WC-Co cermets. The prepared cermets have a mean grain size of less than 0.5 μm even with a pretreatment temperature as high as 1300°C. The WC-10wt.%Co cermet bulk prepared by the optimized milling, pretreatment, and SPS processing achieves excellent mechanical properties with a Vickers hardness of HV 1643, a fracture toughness of 13.1 MPa·m1/2 and a transverse rapture strength of 3100 MPa.

The WC–Co cermet bulks were prepared by spark plasma sintering (SPS) using powder mixtures with different-scaled WC particles. The SPS densification process was studied by calculating the current distribution between the powder sample and the die in the SPS system. The microstructures were characterized and compared for different samples by the WC grain size, Co mean free path and contiguity of WC grains. In spite of a weak effect of WC particle size on the SPS densification stages, the WC particle size plays a significant role in the homogeneity of the cermet microstructure. Good mechanical properties of the SPSed cermet were obtained with an optimized WC and Co particle-size combination. The effects of scale combination of WC and Co particles on the microstructure hence the properties of the SPSed cermet were discussed.

A new way of synthesizing pure WC–Co composite powder by in situ reduction and carbonization reactions of WO2.9, Co3O4 and carbon black powders is presented. The ultrafine-grained cemented carbide bulk has been prepared by spark plasma sintering (SPS) the composite powder. The preparation process, microstructure, and properties of the composite powder and the bulk were investigated and characterized. Both the temperature and time in the present method of combing reduction and carbonization reactions and SPS technique are apparently reduced as compared with the conventional methods. The resultant WC–Co bulk shows a homogeneous fine-grain microstructure and good combined mechanical properties.

The thermodynamics of mechanisms of the reactions in the synthesis processes of WC–Co composite powder by WO3, Co3O4 and carbon as original reactants was investigated. By the thermodynamic calculations, the initiation of the in situ reduction and carbonization reactions, the formation sequence and the relative stability of the reaction products, can be quantitatively described. The formation sequence of the reaction products, and the fact that WC–Co composite powder with pure phases, homogeneous and ultrafine particles can be synthesized at 1323 K in the vacuum condition, as found in experiments, verified the thermodynamic predictions. The thermodynamic analysis performed in the present work is significant to control the preparation processes and to optimize the parameters of fast synthesizing pure-phased WC–Co composite powder.

A novel route for preparing binary amorphous alloy was proposed using Sm–Co system as an example. The alloy ingots with given compositions were used as the parent material. The amorphous intermetallic powder obtained by ball milling the parent alloy was consolidated by the high-pressure spark plasma sintering. The bulk amorphous alloy was detected and confirmed by X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. The present route is potentially applicable to prepare a variety of binary and multicomponent bulk amorphous alloys with adjustable compositions.

A spheroidization processing has been designed for the forged ultrahigh carbon steels (UHCSs) containing Al, in which the mechanism of the divorced eutectoid transformation is applied. Guided by the CALPHAD calculations, the processing is carried out by two periods consisting of austenization at an intermediate temperature in the three-phase(γ + α + cementite)-zone and then isothermal annealing at a temperature a little lower than the critical temperature at which the austenite decomposes completely. The desired microstructure with the fine spheroidal carbides dispersed on the ferrite matrix has been observed, and the well combined mechanical properties, such as the tensile strength Sb = 1050 MPa, the yield strength Ss = 740 MPa, the elongation ratio δ5 = 14% and the reduction of cross-section ψ = 22%, are achieved.

Recrystallization is simulated for a material containing both fine and coarse particles. A deterministic expression is developed for describing the heterogeneous distribution of the stored energy density that arises due to the presence of coarse particles. The effect of recovery reducing the stored energy density, and the different effects of coarse and fine particles on recrystallization are quantified. The criteria for nucleation and growth of the recrystallizing grains are given in energy balances. With 3D Monte-Carlo simulations, various stable recrystallized microstructures are generated by applying different combinations of parameters of the two size classes of particles. In a quantitative study, the effects of recovery and varying volume fractions of the two particle types on the recrystallization kinetics are investigated. The simulation calculations are compared with experimental results obtained with Al–Zr alloys. The model is verified concerning microstructural morphology and recrystallized volume fraction.

A hybrid model that combines first principles calculations and thermodynamic evaluation was developed to describe the thermal stability of a nanocrystalline solid solution with weak segregation. The dependence of the solute segregation behavior on the electronic structure, solute concentration, grain size and temperature was demonstrated, using the nanocrystalline Cu–Zn system as an example. The modeling results show that the segregation energy changes with the solute concentration in a form of nonmonotonic function. The change in the total Gibbs free energy indicates that at a constant solute concentration and a given temperature, a nanocrystalline structure can remain stable when the initial grain size is controlled in a critical range. In experiments, dense nanocrystalline Cu–Zn alloy bulk was prepared, and a series of annealing experiments were performed to examine the thermal stability of the nanograins. The experimental measurements confirmed the model predictions that with a certain solute concentration, a state of steady nanograin growth can be achieved at high temperatures when the initial grain size is controlled in a critical range. The present work proposes that in weak solute segregation systems, the nanograin structure can be kept thermally stable by adjusting the solute concentration and initial grain size.