In the present study, the phase evolution and microstructure of CrMoNbTiW, a new equi-atomic refractory high-entropy alloy, are studied. The alloy was synthesized through mechanical alloying (MA) followed by consolidation using spark plasma sintering. After MA, a major BCC solid solution along with residual Cr and Nb were observed. However, secondary phases such as Laves and carbides were also observed in addition to the major BCC solid solution after sintering. Unsolicited contamination from the milling media is found to be one of the reasons for the formation of secondary phases. The high hardness of 8.9 GPa after sintering was attributed to the presence of secondary phases along with the nanocrystalline nature of the alloy. To understand the phase evolution, calculation of phase diagram was carried out using CALPHAD. Further, binary phase diagram inspection and simple empirical parameters were also used to assess their effectiveness in predicting phases.

Earth stabilization, using two by-products available in Burkina Faso: Calcium Carbide Residue (CCR) and Rice Husk Ash (RHA), improved the performance of compressed earth blocks (CEBs). The effect of adding CCR or CCR: RHA (in various ratios) to the clayey earth was investigated. CEBs were molded by manually compressing moisturized mixtures of earthen materials and 0-15 % CCR or CCR: RHA (various ratios) with respect to the weight of earthen material. The results showed that, with 15 % CCR: RHA in 7: 3 ratio, the compressive strength of CEBs (6.6 MPa) is three times that of the CEBs containing 15 % CCR alone (2.2 MPa). This improvement was related to the pozzolanic reaction between CCR, clay and RHA. These CEBs comply with the requirement for wall construction of two-storey housing.

Understanding the precipitation of brittle hydride phases is crucial in establishing a failure criterion for various zirconium alloy nuclear fuel cladding. Accordingly, it is important to quantify the sensitivity of hydride precipitation to the component microstructure. This experimental investigation focuses on two microstructural characteristics and their role as hydride nucleation sites: The grain size and the alloy chemical composition. Samples of commercially pure zirconium (Zr-702) and Zircaloy-4, each with a wide range of grain sizes, were hydrided to 100 ppm and micrographs of the hydride distribution were optically analyzed for inter-granular and intra-granular precipitate sites. For most grain sizes, it was found that a significantly lower fraction of the precipitated hydrides nucleated at grain boundaries in Zircaloy-4 than in Zr-702, suggesting that a higher SPP content encourages the formation of intra-granular hydrides. Moreover, this effect became more prominent as the grain size increased; large-grain specimens contained a higher fraction of intra-granular hydrides than small-grain specimens of both Zr-702 and Zircaloy-4, highlighting the potency of grain boundaries as nucleation sites and how SPPs can influence the hydride distribution profile.

The efficiency of Cu(In,Ga)Se2 (CIGS)-based solar cells could be continuously increased up to 22.6% by employing alkali metal dopants like Na, K, Rb, and Cs. The alkali metals are supplied to the CIGS layer from the glass substrate during deposition, from precursor layers or by a post deposition treatment. The alkali metal distribution in CIGS is not homogenous. Independently of the alkali metals used, their concentration at grain boundaries is much higher than that inside the grains. In this contribution, we discuss thermodynamic limitations for alkali metals in CIGS and show that in higher concentrations they are responsible for secondary phase separation. Applying the concept of immiscibility of phases for alkali metals in CIGS, we suggest how segregation at grain boundaries, formation of clusters in CIGS grains, sporadic formation of microstructures in the CIGS layer (hotspots, nodules), and separation of secondary phases with ordered structures can be interpreted.

Age-hardening of homogenized and cold-rolled invar-based Sn alloys results in the development of continuously-formed (CP) and discontinuously-formed (DP) Ni3Sn2 precipitates. In situ investigation of the DP reaction front (RF) velocity (V) revealed a nonsteady-state behavior upon early aging stages followed by a constant V after prolonged aging. The reason for the initial nonsteady-state behavior was experimentally studied and attributed to the reduction of matrix Sn-supersaturation ahead of the DP RF as a result of the simultaneous CP coarsening (in homogenized specimen) or the CP increased volume fraction (in cold-rolled specimen). A similar trend of V variation in the homogenized specimen was obtained after the modification of the original Hornbogen model for the nonsteady-state DP growth kinetics. In general, variations of the transformed matrix fraction via the DP reaction suggest the faster kinetics of this reaction in cold-rolled specimen as compared to the homogenized one due to the existence of more nucleation sites induced by the cold deformation.

The Cu–S compounds have been reported as promising thermoelectric materials with abundant element composition, low price, and low toxicity. In this work, Sn x Cu1.8−x S samples with different Sn contents (x = 0.005, 0.01, 0.03, and 0.05) were fabricated by mechanical alloying combined with spark plasma sintering. The phase structure and microstructure of all the bulk samples were checked by X-ray diffraction (XRD) and field emission scanning electron microscopy respectively. The thermoelectric transport properties, such as electrical conductivity, Seebeck coefficient, carrier concentration, carrier mobility, and thermal conductivity, were measured. The effect of second phase introduced by Sn addition on the thermoelectric properties of Cu–S system was investigated. The thermoelectric properties of samples were improved by the precipitations of two different second phases (Cu2SnS3 and Cu4SnS4). The second phase species depend on the Sn contents. Finally, the Sn0.01Cu1.79S bulk sample obtained the highest ZT value of 0.81 at 773 K, which is 1.6-fold higher than that of the pristine Cu1.8S sample due to the significantly reduced thermal conductivity by second phase and nanopores scattering.

Thermal stability up to 400 °C of nanocrystalline (NC) Ni electrodeposits (EDs) with a mean grain size of 28 nm and dispersions of a small amount of CeO2 nanoparticles has been investigated by comparing with two CeO2-free NC Ni counterparts, one with a slightly smaller mean grain size of 18 nm and the other with a slightly larger mean grain size of 34 nm. The results show that the co-deposition of CeO2 particles has dual effects on the thermal stability of the NC Ni EDs, i.e., it promotes the grain growth at the beginning but retards subsequently. It is proposed that the CeO2 co-deposition leads to a decrease in sulfur level and an increase in the plane defects as a result of introduction of incoherent Ni/CeO2 interfaces, which play dominant roles in the grain growth at low temperatures; while the drag effect of CeO2 dispersions becomes dominant at higher temperatures.

Carbon nanotube (CNT) sock formation is required for the continuous synthesis of CNT thread or sheet using the gas phase pyrolysis method. Nanometer diameter CNTs form and are carried along the reactor tube by gas flow. During the flow, the CNT stick to each other and form bundles of about 10-100 nm diameter. Coupling of the CNT bundles in the flow leads to the formation of a centimeter diameter CNT sock with a wall that is hundreds of nanometers thick. Understanding the multiscale phenomena of sock formation is vital for optimizing the CNT synthesis and manufacturing process. In this work, we present a multiscale model for the CNT bundle agglomeration inside a horizontal gas phase pyrolysis reactor. The interaction between CNT bundles was analyzed by representing the attraction forces between CNTs using a discrete phase modeling method. Flow in the synthesis reactor was studied using a computational fluid dynamics (CFD) technique with multiphase flow analysis. A model was proposed to represent the coupling between CNT bundles and the gas flow. The effect of different CNT bundles on the agglomeration phenomenon was analyzed. The modeling results were also compared with experimental observations.

The pitting corrosion resistance of AL-6XN PLUS™ superaustenitic stainless steel, 304L, 316L, and 317L austenitic stainless steels was investigated using the cyclic polarization technique. These materials were evaluated in the as received condition and heat-treated at temperatures between 500 °C and 900 °C for 72 h. A thermodynamic simulation was performed using the software Thermocalc® to predict possible deleterious phases in selected temperatures. The simulations have predicted the sigma phase in the selected temperature range. An aqueous solution of sulfuric acid and sodium chloride was used as electrolyte in the corrosion tests. The results showed that pitting corrosion was not observed on the samples of AL-6XN PLUS™ steel. The 304L steel suffered pitting corrosion. All the polarization curves of this steel showed hysteresis characteristics of pitting corrosion. The 316L and 317L steels were resistant to pitting corrosion, but susceptible to crevice corrosion.

The effect of annealing treatment on the microstructures, mechanical, and wear properties of a CuZnAlMnSiNiCr brass alloy is investigated. The results indicate that nanosized Mn5Si3 particles are observed to precipitate from the β phase at temperatures above 750 °C. After annealing at 800 °C for 4 h, the formation of finely, coherent precipitates dispersed within the matrix results in the great improvement of strength, hardness and thus the high wear resistance, which can be proven by the decreased wear rates and friction coefficients. According to the examination of the wear topography, adhesive, abrasive, and oxidative wear are found to be the major wear forms during the dry sliding wear. After the precipitation-hardening treatment, the adhesion and abrasion decrease, and few spallings and cracks are observed on the worn surfaces. In addition, the wear behavior of the alloy is found to be strongly dependent on its strength and hardness.

The effect of solution treatment (ST) on the microstructure and mechanical properties of cast Al–3Li–1.5Cu–0.2Zr alloy was investigated. Results showed that the volume fraction of secondary phases (Al2Cu, Al3Li) decreased obviously after ST. It was found that the strengthening of Al–3Li–1.5Cu–0.2Zr alloy was a balance of the precipitation strengthening, residual phase strengthening and fine grain strengthening. The residual phase strengthening and fine grain strengthening decreased with increasing the solution temperature and time, while precipitation strengthening increased. After ST at 560 °C for 40 h, the elongation of Al–3Li–1.5Cu–0.2Zr alloy reaches the highest value of 22.1%. In addition, the tensile properties are up to the highest values, ultimate tensile strength of 359 MPa and elongation of 3.5% after optimal ST at 560 °C for 40 h followed by aging treatment.

The development of high performance Al–Cu based alloys generally depends on the strict control of the Fe content. However, with the increasing use of recycled aluminum alloys, it is necessary to increase the tolerance for the Fe content in Al–Cu cast alloys for the purpose of low cost, energy saving, and environment protection. In this study, the formation of Fe-rich intermetallics and their effect on the tensile properties of squeeze-cast Al–5.0 wt% Cu–0.6 wt% Mn alloys with an Fe content of up to 1.5 wt% have been investigated. The full formation sequence of squeeze-cast Al–5.0 wt% Cu–0.6 wt% Mn alloys with different Fe contents has been established. The results were also compared with the corresponding results obtained for Al–5.0Cu–0.6Mn alloys prepared by gravity die casting. It is found that the Fe-rich intermetallic compounds mainly consist of α-Fe and β-Fe in alloys with a low Fe content, changing into Al6(FeMn) and Al3(FeMn) for alloys with a high Fe content. The applied pressure promotes the formation of the Fe-rich intermetallics α-Fe/Al6(FeMn) and prevents the precipitation of needle-like β-Fe/Al3(FeMn). The elongation of the alloys gradually decreases with the Fe content, and a maximum value for both the ultimate mechanical strength and the yield strength was found for the alloys with 0.5 wt% Fe. The tensile properties of alloys with a different Fe content significantly increased as the applied pressure was increased from 0 to 75 MPa, especially the elongation.

The variation of properties and evolution of microstructure of Cu–10Ni–3Al–0.8Si alloy during isothermal and aging treatment was studied. The time–temperature–property curves of the alloy were established. The nose temperature of the alloy was about 662 °C, and the alloy presented high quench sensitivity when quenched in the nose temperature zone. Discontinuous precipitation occurred when Cu–10Ni–3Al–0.8Si alloy was isothermally treated at 550 °C, and the discontinuous precipitates at the grain boundary became coarse when the isothermal temperature increased to 650 °C. Further increasing the isothermal temperature to 750 °C, cellular precipitation occurred in the alloy. Both Ni3Al precipitates with L12 ordered structure and δ-Ni2Si precipitates with DO22 ordered structure precipitated in the isothermally treated Cu–10Ni–3Al–0.8Si alloy. The orientation relationships between the precipitates and matrix were determined as ${[001]_{{\rm{Cu}}}}{\left\| {{{[001]}_{{\rm{N}}{{\rm{i}}_3}{\rm{Al}}}}\left\| {[001]} \right.} \right._\delta }$, ${(110)_{{\rm{Cu}}}}{\left\| {{{(110)}_{{\rm{N}}{{\rm{i}}_3}{\rm{Al}}}}\left\| {(010)} \right.} \right._\delta }$, and ${(1\bar 10)_{{\rm{Cu}}}}\left\| {{{(1\bar 10)}_{{\rm{N}}{{\rm{i}}_3}{\rm{Al}}}}} \right\|{(100)_\delta }$.

The interface with reactive transport models used in performance assessment calculations is described to identify aspects of the glass waste form degradation model important to long-term predictions. These are primarily the conditions that trigger the change from the residual rate to the Stage 3 rate and the values of those rates. Although the processes triggering the change and controlling the Stage 3 rate are not yet understood mechanistically, neither appears related to an intrinsic property of the glass. The sudden and usually significant increase in the glass dissolution rate suggests the processes that trigger the increase are different than the processes controlling glass dissolution prior to that change. Application of a simple expression that was derived for mineral transformation to represent the kinetics of coupled glass dissolution and secondary phase precipitation reactions is shown to be consistent with experimental observations of Stage 3 and useful for modeling long-term glass dissolution in a complex disposal environment.

Aiming to clarify the effects of initial states on hot deformation behavior of a powder metallurgy nickel-based superalloy FGH96, specimens in hot isostatic pressed (HIPed) and solution states were isothermally compressed in the temperature range of 1000–1150 °C and the strain rate range of 0.001–1.0 s−1. It revealed that the flow behavior of FGH96 was dependent on the initial states, in which the deformation resistance was higher in the solution state than that in the HIPed state at evaluated temperatures, and the differences became less when the temperature was higher than the γ′ dissolution temperature. The calculated hot activation energy using peak stresses are 590 and 1285 kJ mol−1 for HIPed and solution specimens. Comparison with HIPed specimen, the efficiency of power dissipation (η) in solution specimen is less, and the optimum workability regime moves to higher temperatures. Cracking and in-grain shear bands were observed in the specimens when compressed in flow instability areas.

The effect of the intercritical temperature on the microstructure and mechanical properties of a newly developed quenching and partitioning steel using martensitic microstructure prior to the heat treatment process was studied. Such a quenching and partitioning process possessed a unique microstructure evolution, especially during intercritical annealing after prequenching. Excellent mechanical properties were obtained due to this unique multiphase microstructure. Significant amount of interlath-retained austenite was acquired and the relationship between the microstructure and work-hardening behaviors was proposed. The martensite/austenite islands increased at elevated annealing temperature, which deteriorated the total elongation and increased the tensile strength as hard constituents when it was excessive. The result indicated that the present full martensitic microstructure before the intercritical annealing is probably more suitable to an industrial application and is a better way to produce high strength steels with suitable ductility.

In this study, the precipitation behavior of the pretwinned extruded Mg–6Al–1Zn alloy was investigated. It was observed that the precipitates preferentially nucleated at the twin boundaries or within the preexistent twins. This distribution of the precipitates led to the distinguishing influences on subsequent compression and tension process, which were dominated by twinning and detwinning of the preexistent twins, respectively. The compressive yield strength after aging was a little lower than the stress when the precompression was interrupted, which meant that the impeding effect of precipitation on twin expansion was relatively smaller than that of dislocations induced by precompression. However, the tensile yield strength of aged samples was extremely higher than that of non-aged samples as the migration of the twin boundaries during detwinning was considerably hindered because of the preferential precipitation within the preexistent {10-12} twins.

Tungsten carbide (WC) particle–reinforced iron matrix surface composites with different content of Cr were fabricated using vacuum evaporative pattern casting technique. It was found that the morphology of carbides changed from continuous net-shape to isolated block-shape patterns. The amount of carbides increase with the increasing Cr content in the matrices. Composites with different Cr content show better abrasive wear resistance than those without Cr. With the increase of Cr content in the matrices, the three-body abrasive wear resistance of the composites increased, while the impact abrasive wear resistance of the composites increased under 1 J impact load, but first increased and then decreased under 3 J impact load. The influences of the addition of Cr in the matrices on the abrasive wear resistance were the synergistic effects of two protecting effects and two supporting effects. The results might provide significant references for the design and practical application of WC particle–reinforced iron matrix surface composites.

The formation of uranyl peroxide phases was identified as a corrosion product of spent fuel by Hanson et al [1]. The subsequent analysis of this phase showed that metastudtite retained 241Am, 237Np and 239Pu [2]. In this study, the retention of radionuclide Pu4+ and An3+, released from the spent fuel matrix into studtite structure, has been evaluated by the precipitation of studtite from uranyl dissolution with variable concentrations of REE (Th, Nd, Sm and Eu). Three different precipitation conditions parameters were studied: media of synthesis, time of synthesis and REE concentration. Synthesized phases were characterized by XRD and the cell parameter was calculated. The REE incorporation was determined by ICP-MS analysis. The results showed that studtite could incorporate 63% of Th in solution during its precipitation. Changes in the “a” cell parameter were identified. The results suggest that studtite coprecipitated with REE could play a role as a limiting for the REE mobility.

Under a creep condition of relatively intense stress, dispersive precipitation of TiC nanoparticles could be promptly brought out within the austenite grain when the iron-nickel-base superalloy was fabricated through the specific production of the ingenious alloy design, applicable electro-slag remelting and high-temperature solution-anneal developed in this study. Both the TiC and coexistent M23C6 precipitates are cubo-octahedral in shape, remaining the cube-to-cube orientation relationship and coherent {111}carbide/γ and {100}carbide/γ interphase interface with the austenite, which bring about the dispersion-strengthening effect so that the time to rupture for the present alloy could be increased by 1.8 times of magnitude relative to the commercial creep-resistant product of the same grade. The improved creep property can be attributed to the mechanism that the nanometer-scale intragranular TiC and submicron intergranular M23C6 can act as pinning points for individual dislocations and grain boundaries, respectively, resulting in the raised Orowan strengthening and suppressed grain boundary sliding. Since the strengthening media found in this study are thermally stable and able to emerge readily prior to the formation of γ’ phase at the temperature range studied, this work suggested an improved grade of heat resistant alloy for applications in a relatively harsh environment that the creep lifetime might be shorter than the incubation period of the common strengthening phase for superalloys.