We introduce general estimation and inference methods for threshold spatial panel regression with two-way fixed effects in a diminishing-threshold-effects framework. A valid objective function is obtained through a simple adjustment on the concentrated quasi loglikelihood with fixed effects being concentrated out, which leads to a consistent estimation of all common parameters. We show that the estimation of threshold parameter has a negligible effect on the asymptotic distribution of the main parameter estimators and thereby regular inference methods apply, though a bias correction may be necessary. The limiting distribution of the threshold parameter estimator is shown to be non-regular and infeasible, and for inference, a likelihood ratio test procedure is proposed. The test for the non-existence of threshold effects faces an identification issue at the null. To overcome this difficulty, we propose a sup-Wald test and a bootstrap method for its critical values. Monte Carlo results show that the proposed methods perform well in finite samples. An empirical application is presented on age-of-leader effects on political competitions across Chinese cities.

We consider estimation and inferences for general spatial panel data models with randomly missing observations on responses. It allows for unobserved spatiotemporal heterogeneity, time-varying endogenous and contextual spatial interactions, time-varying cross-sectional error dependence, and serial correlation. A general M-estimation method is proposed for model estimation and a novel corrected plug-in method is proposed for model inference. Both take into account the estimation of fixed effects. Asymptotic properties of the proposed methods are studied, and finite sample properties are investigated. An empirical application is given using U.S. state tax competition data. The proposed methods apply to matrix exponential spatial specification and can be further extended to include higher-order spatial effects.

Abstract Refractory high-entropy alloys (RHEAs) hold promise for applications in extreme environments. However, conventional as-cast RHEAs are constrained by the trade-off between strength and ductility, necessitating time- and energy-intensive post-processing. Here, we propose a streamlined strategy to fabricate RHEAs via laser directed energy deposition (LDED) using elemental powder blends, eliminating the need for post heat treatments. The additively manufactured (AMed) Nb40Ta25Ti15Hf15Zr5 alloy, characterized by a high density of intrinsic edge dislocations introduced during the thermal cycling of the process, demonstrates a remarkable tensile strength of ~497.3 MPa and a uniform elongation of ~6.8 % at 1000 °C, representing a ~ 37.8% and ~61.9% increase, respectively, over its as-cast counterparts. It is found that the intrinsic edge dislocations generated during AM process significantly enhances the alloy’s strain hardening capability at elevated temperatures. Simultaneously, the high density of edge dislocations effectively enhance material deformability through kink band formation and the stochastic nature of dislocation motion. This work presents a cost-effective pathway for the rapid fabrication of AMed RHEAs with an exceptional combination of high-temperature strength and ductility, paving the way for next-generation structural alloys in extreme environments.

Multilevel gradient microstructures and twins are successfully introduced into laser additive manufactured CoCrFeNi high entropy alloy using synchronous ultrasonic impact treatment method. Severe plastic deformation was introduced in the previously deposited layer synchronously treated by ultrasonic impact treatment, creating the following microstructures named surface fine-grain layer, high-deformed layer as well as deformation twins. Recrystallization occurred during the subsequent laser deposition process, resulting in the formation of recrystallized regions and annealing twins. With ultrasonic impact treatment, the average microhardness of about 243.4 HV0.2 was achieved, which was about 43.4 % higher than the conventional specimen. The coefficient of friction was reduced from 0.94 to 0.85, while the wear rate was reduced by 71.7 %. Molecular dynamics simulations showed that the presence of twins significantly affects the dislocation evolution behavior and improves the wear resistance of CoCrNiFe high entropy alloy. This work combines the benefits of cold working and heat treatment via integrating synchronous ultrasonic impact treatment into the direct energy deposition process to fabricate high-entropy alloys with refined microstructure as well as enhanced surface properties, without altering the material composition.

Intrinsic defects and immiscibility-driven segregation fundamentally limit the joining reliability of additively manufactured dissimilar-metal composites. Here, deep-penetration laser welding is used to join selective laser melting-fabricated 316L/CuSn10/316L laminated structures, aiming to elucidate how melt-pool dynamics govern defect elimination and mechanical performance. The results show that sufficiently high and stable heat input establishes a highly convective molten pool dominated by Marangoni flow, which actively annihilates native volumetric defects and heals interfacial cracks, increasing the relative density from similar to 98% in the as-built state to 99.86%. Concurrently, the coupled action of recoil pressure and surface-tension gradients induces macroscopic liquid-liquid phase separation, driving Cu-rich liquid toward the weld periphery. The resulting phase redistribution and spheroidization of the Cu-rich phase suppress deleterious grain-boundary wetting and liquation cracking. An asymmetric interfacial response is established, characterized by epitaxial growth on the 316L side and grain refinement on the CuSn10 side, while a coherent or semi-coherent gamma-Fe/alpha-Cu interface with a specific [-110] orientation relationship ensures robust metallurgical bonding. Consequently, the joint exhibits a superior strength-ductility synergy, achieving a tensile strength of 656.7 MPa with an elongation exceeding 25%, governed by a stress accommodation, load transfer-dominated failure mechanism. This work establishes a unified mechanistic framework linking defect inheritance, melt-pool-driven healing, phase separation, and mechanical response, providing general guidance for joining AM dissimilar-material systems.

We propose an M-estimation method for dynamic spatial panel data models with interactive fixed effects based on (relatively) short panels. Unbiased estimating functions are constructed by adjusting the concentrated conditional quasi scores, given the initial values and with the factor loadings being concentrated out, to account for the effects of conditioning and concentration. Solving the estimating equations gives the M-estimators of the common parameters and common factors. Under fixed T, root n-consistency and joint asymptotic normality of the M-estimators are established. Under T = o(n), the M-estimators of the common parameters are shown to be root nT-consistent and asymptotically normal. For inference, difficulty lies in the estimation of the variance-covariance (VC) matrix of the estimating functions. We decompose the estimating functions into a sum of n nearly uncorrelated terms, using their outer products with a covariance adjustment to obtain a consistent VC estimator under both fixed T and T = o(n). Monte Carlo results show that the proposed methods perform well in finite samples. We apply our methods to examine peer effects in firms' innovation decisions, using data from publicly listed Chinese firms. The results reveal significant spillovers in R & D investment within industries and spatial correlations in unobserved shocks among geographically proximate firms.

WC particles reinforced CoCrFeNiMo high-entropy alloy (HEA) composite coatings were prepared on Cr12MoV steel successfully by laser cladding technology to improve the wear resistance of substrates. Effect of WC content on microstructure and wear property of the composite coatings was studied in detail. Large numbers of carbides with four main types: primary carbide crystals, eutectic structures, massive crystals growing along the periphery of the remaining WC particles and incompletely fused WC particles, were found to exist in the WC/CoCrFeNiMo composite coatings. With increasing WC content, the microhardness of coatings is gradually improved while the average friction coefficients follow the opposite trend due to solid solution strengthening and second phase strengthening effect. The maximum microhardness and minimum friction coefficient are HV0.2 689.7 and 0.72, respectively, for the composite coating with 30 wt.

We develop new tests of clustered equal predictive ability (C-EPA) in panels where the clusters are unknown and estimated by a Panel Kmeans algorithm. This algorithm differs from the standard Kmeans algorithm by employing the time series variation of the panel rather than relying merely on time averages of observations. To address the challenge of testing hypotheses that depend on data-driven cluster estimates, we adopt a selective conditional inference framework. Specifically, we derive a Wald-type test statistic for pairwise equality and show that the limiting distribution of its square root conditional on the estimated cluster structure is that of a truncated χ random variable. We characterize the associated truncation set as a polyhedron in the data space. As a test of the C-EPA hypothesis, we propose a p-value combination method which aggregates the evidence against the pairwise equality and overall EPA null hypotheses. In addition, we prove that using an information criterion to select the unknown number of clusters under the alternative hypothesis prior to testing does not require further conditioning to obtain a valid test. Monte Carlo simulations confirm the excellent finite sample performance of the proposed tests. An empirical application to forecasting exchange rates using traditional time series models as well as machine learning methods illustrates the practical importance of our procedure.

We consider spatial panel data models with genuine unbalancedness arising from the non-presence of some spatial units in certain time periods. General M-estimation methods are proposed for model estimation, which take into account the estimation of the incidental fixed effects parameters and allow for spatiotemporal heteroskedasticity and high-order time-varying spatial effects. Corrected plug-in methods are proposed for standard error estimation. The proposed estimation and inference methods are rigorously studied for their asymptotic properties and finite sample performance. An application to China's provincial FDI inflows shows that properly accounting for genuine unbalancedness uncovers significant positive spatial spillovers that are masked when the data are artificially treated as balanced.

Synchronous ultrasonic impact treatment (UIT) is proposed to enhance the microstructure and wear property of laser cladded CoCrFeNiMo high entropy alloy (HEA) coatings on 45 steel. FCC phase with minor tetragonal sigma phase and rhombic eta phase are form in both conventional and UIT treated coatings. Due to the plastic deformation and high-frequency vibrations induced by UIT, dislocation interactions lead to recrystallization process at the top region coating. With the application of UIT, the columnar grains at top region of the coating transform into fine equiaxed grains owing to recrystallization. The fragmentation of dendrites occurs in the middle region of the coating, resulting in reduced dendrite arm spacing. The results also show the defects, such as pores and microcracks, are effectively eliminated within the coating. Microhardness and wear property of the coating are remarkably enhanced owing to fine-grain strengthening and second-phase strengthening. The average friction coefficient decreases from 0.56 for the conventional sample to 0.49 for the UIT treated sample, and the wear mechanism evolved from a combination of abrasive, fatigue, and oxidized wear to predominantly fatigue and oxidized wear. It indicates that synchronous ultrasonic impact assisted laser cladding is a potential method to fabricate high-performance HEA coatings.

TiC-TiB-Cr2B3 multiphase-ceramic via in-situ reaction synthesis between Ti and B4C particles was proposed to enhance the wear property of laser cladded Al0.5CoCrFeNi high-entropy alloy coating on 304 steel. The effect of Ti and B4C particles content on phase, microstructure and wear property of composite coatings were studied in detail. The Tix(B4C)yAl0.5CoCrFeNi composite coatings all form a good metallurgical bond with substrate. Tix(B4C)yAl0.5CoCrFeNi coatings are mainly composed of equiaxed FCC phase matrix, intergranular Ti and Cr borides and TiC particles. With increasing Ti and B4C content, the proportion of FCC gradually decrease, while TiC-TiB-Cr2B3 ceramic phases gradually increase. Meanwhile, due to second phase strengthening, solid solution strengthening and fine crystal strengthening effect, the microhardness and wear resistance of Tix(B4C)yAl0.5-CoCrFeNi coatings increases significantly. The maximum microhardness value, minimum friction coefficient and wear rate of 423.5HV0.2, 0.53 and 1.99 x 10-4 mm-3/N & sdot;m, respectively, is obtained when x = 1 and y = 0.2 are selected, and the main wear mechanisms of the composite coating are adhesive wear and oxidative wear. The proposed TiC-TiB-Cr2B3 multiphase-ceramic induced by in-situ reaction synthesis of Ti and B4C particles offers a potential approach to enhancing the wear resistance of high entropy alloy coating by laser cladding.

We propose two types of equal predictive ability (EPA) tests with panels to compare the predictions made by two forecasters. The first type, namely S-statistics, focuses on the overall EPA hypothesis which states that the EPA holds on average over all panel units and over time. The second, called C-statistics, focuses on the clustered EPA hypothesis where the EPA holds jointly for a fixed number of clusters of panel units. The asymptotic properties of the proposed tests are evaluated under weak and strong cross-sectional dependence. An extensive Monte Carlo simulation shows that the proposed tests have very good finite sample properties even with little information about the cross-sectional dependence in the data. The proposed framework is applied to compare the economic growth forecasts of the OECD and the IMF, and to evaluate the performance of the consumer price inflation forecasts of the IMF.

To reduce wear and energy loss during the movement of miniaturized devices such as wearable devices and MEMS, and to address the inherent limitations of individual categories of solid lubricating materials, a new MXene-based composite solid lubricating material was designed. In this study, Ti3C2Tx@MoS2 composites were successfully prepared via hydrothermal synthesis, with MoS2 nanosheets grown uniformly on the surface and interval of the multilayer Ti3C2Tx. The composites were deposited as a solid lubricant coating on silicon substrates using a drop coating method. Tribological behavior was evaluated by ball-on-disk reciprocating and rotating tribometer, respectively. The results revealed that the friction coefficients of the multilayer Ti3C2Tx@MoS2 composite coatings were reduced by 75%, 69%, and 58%, respectively, compared to the multilayer Ti3C2Tx, MoS2, and their mechanical mixtures. Moreover, this study proposed the excellent wear resistance of the multilayer Ti3C2Tx@MoS2 composite coatings was attributed to the synergistic lubrication of Ti3C2Tx and MoS2. MoS2 was enriched in the wear track, and the tribofilm formed during friction process played the role of friction reduction and lubrication. In comparison, the multilayer Ti3C2Tx had an excellent effect on the wear resistance and structural support.

Synchronous ultrasonic impact treatment is proposed to induce recrystallization and twinning of laser directed energy deposited CoCrFeNi high entropy alloy, which remarkably refine microstructure and enhance the mechanical properties of deposited alloy. The mechanism of ultrasonic impact influence on microstructure has been investigated through multi-scale characterization, and the contribution of multiple mechanisms to the strength has also been discussed in detail. Ultrasonic impact causes intense plastic deformation of the previously deposited layer, recrystallization occurs during the sequent directed energy deposition process, the average grain size reduces by 74%, meanwhile, annealing twins are generated. Ultimate tensile strength and yield strength of deposited sample increase dramatically while maintaining the plasticity. Dislocation strengthening, grain boundary strengthening and unique annealing twins strengthening contribute to the yield strength enhancement, and the related strengthening contribution are calculated as 49MPa, 50MPa and 44MPa, respectively. Molecular dynamics calculations reveal the presence of annealing twins has a detrimental effect on the growth of deformation twins while it is beneficial to the dislocation multiplication due to more sources of dislocations and additional activation of slip systems during tensile test. The proposed recrystallization and twinning induced by ultrasonic impact offer a novel approach to improving the microstructure and mechanical properties of high entropy alloys by laser directed energy deposition.

To improve the friction and wear performance of coatings in aerospace engineering under wet and dry alternating conditions, the porous hard TiCN coating was prepared by a combination of multi-arc ion plating and oblique angle deposition. The study found that when the titanium target current was reduced from 80 A to 60 A, the pore size of the porous TiCN coating increased from 0.30 mu m to 0.93 mu m. In comparison to the low hardness of stainless steel substrate of 3.4 GPa, the hardness of TiCN coatings with pore sizes of 0.93 and 0.30 mu m rose to 10 and 22 GPa, respectively. The existence of pores can effectively improve the hydrophilicity of the coatings. However, as the pore size increased, the anti-wear lifetime of the coatings were also decrease. This process was followed by ultrasonication and hydrogen reduction of (NH4)2MoS4 to infuse MoS2 directly into the pores to fabricate the TiCN-MoS2 composite coatings. The findings revealed MoS2 atomic sheets are randomly embedded in the pores of the TiCN coating. In a stable humidity environment, as the relative humidity increased, the friction coefficient of the TiCN-MoS2 porous composite coating increased and the anti-wear lifetime decreased. In addition, the anti-wear lifetime of the TiCN-MoS2 porous composite coating at 20 % relative humidity environment is 128,322 laps, which exceeded the 38,099 laps of the dense TiCN-MoS2 composite coating. This proved that the porous composite coating had better anti-wear lifetime due to the continuous release of MoS2 in the pores under low humidity conditions. The tribological behavior of the porous composite coatings was systematically investigated under alternating humidity conditions, with a comparison against the dense TiCN-MoS2 composite coatings. The porous composite coatings possessed better self-adaptation under alternating humidity conditions, with coefficients of friction of 0.05 and 0.15 at 10 % and 70 % RH air, respectively. A detailed discussion was conducted on the relationship between tribofilm composition and tribological properties under different humidity environments.

Case teaching, through the selection and analysis of a series of cases, provides scenes close to students, which are easy for students to understand and think, enhance students’ ability to understand and analyze knowledge, and improve their ability to use the knowledge and comprehensive quality. In order to improve the teaching quality of Modern Analytical Methods of Materials and Chemical Industry and make students understand the relationship between teaching content and actual style analysis, the teachers carried out case teaching to ensure the teaching effect and lay the foundation for training practical talents in the field of materials and chemical industry.

The laser cladding technique with and without ultrasonic vibration was employed to prepare Fe-based crystal-line/amorphous composite coatings and the effect of ultrasonic vibration on the evolution of microstructures and microhardness was investigated via SEM observation and microhardness testing. The results show that, during the laser cladding process assisted with ultrasonic vibration, the content of amorphous phase is increased by 1.4 % and the growth of columnar crystals at interface is inhibited. The average length of columnar crystal at interface is measured to be around 17.2 +/- 5.1 mu m which is diminished by 35.8 %, and the microhardness of coating is about 866.2 +/- 57.5 HV0.2 which is improved by 27.9 % compared to that without ultrasonic vibration.

Ti-6Al-4V(TC4) titanium alloy is a kind of α+β type two-phase titanium alloy widely used. However, due to the microscopic defects in additive manufacturing titanium alloy, its mechanical properties are lower than the forging level, and post-treatment is usually required. Therefore, it is necessary to further study the additive manufacturing process and post-treatment of TC4 titanium alloy. In this paper, the microstructure and comprehensive properties of titanium alloy were analyzed by the changes of common process parameters such as energy input power and scanning strategy in the additive manufacturing process, and the influence of other process parameters such as protective gas type, substrate thickness, powder size and other factors in the additive manufacturing process was introduced. The influence of common heat treatment methods after additive manufacturing on its microstructure and mechanical properties was also comprehensively analyzed, and the influence of new post-heat treatment methods, such as vacuum heat treatment and cyclic heat treatment, as well as the influence of multiple post-treatment and comprehensive use of heat treatment were summarized. Generally speaking that the reasonable selection of additive manufacturing process parameters and the application of post-heat treatment method are the basis for obtaining titanium alloy components with excellent performance. The comprehensive use of various heat treatment methods or other post-treatment methods and heat treatment are the effective ways to further improve the performance of titanium alloy components in additive manufacturing. To establish a uniform selection standard for additive manufacturing process parameters and post-processing process is the key to the future development of additive manufacturing.

Metal foam composite is a kind of lightweight composite with low density, high strength, high shielding performance, high damping performance and other characteristics. It has a wide range of application prospects in aerospace, drilling trap floats, artificial bone and other fields, which has attracted people's attention. In this paper, based on the research of the existing literature, the fabrication methods of metal foam composites were introduced, the effect of microstructure on the properties of metal foam composites was analyzed, the progress of mechanical properties, damping properties, shielding properties and heat insulation and their mechanisms of metal foam composites and their applications in relevant fields were reviewed, which provides a theoretical basis for the development of metal foam composites in the future, and the new fabrication technology, modeling research, sandwich structure of metal foam composites and the fabrication of high performance foam hollow sphere composite were also prospected.