The Synergy Reinforcement Effect of Sm0.85Zn0.15MnO3 and ZrMgMo3O12 on Sm0.85Zn0.15MnO3-ZrMgMo3O12/Al-20Si Composites.

Negative thermal expansion (NTE) ceramics Sm0.85Zn0.15MnO3 (SZMO) and ZrMgMo3O12 (ZMMO) were selected to prepare Sm0.85Zn0.15MnO3-ZrMgMo3O12/Al-20Si (SZMO-ZMMO/Al-20Si) composites using ball milling and vacuum heating-press sintering processes in this study. The synergistic effect of the SZMO and ZMMO NTE ceramic reinforcements on the microstructure, mechanical properties, and coefficient of thermal expansion (CTE) of the composites was investigated. The results show that the processes of ball milling and sintering did not induce the decomposition of SZMO or ZMMO NTE ceramic reinforcements, nor did they promote a reaction between the Al-20Si matrix and SZMO or ZMMO NTE ceramic reinforcements. However, the excessive addition of SZMO and ZMMO NTE ceramics led to their aggregation within the composite. Adding a small amount of SZMO in combination with ZMMO effectively increased hardness and yield strength while reducing CTE in the Al-20Si alloy. The improvement in strength was primarily provided by SZMO, while the inhibition effect on CTE was primarily provided by ZMMO. An evaluation parameter denoted as α was proposed to evaluate the synergy effects of SZMO and ZMMO NTE ceramic reinforcements on the mechanical properties and CTE of the composites. Based on this parameter, among all composites fabricated, adding 2.5 vol% SZMO NTE ceramic and 10 vol% ZMMO NTE ceramic resulted in an optimal balance between CTE and strength for these composites with a compressive yield strength of 349.72 MPa and a CTE of 12.55 × 10-6/K, representing a significant increase in yield strength by 79.20% compared to that of Al-20Si alloy along with a notable reduction in CTE by 26.44%.

The Primary Irradiation Damage of Hydrogen-Accumulated Nickel: An Atomistic Study.

Nickel-based alloys have demonstrated significant promise as structural materials for Gen-IV nuclear reactors. However, the understanding of the interaction mechanism between the defects resulting from displacement cascades and solute hydrogen during irradiation remains limited. This study aims to investigate the interaction between irradiation-induced point defects and solute hydrogen on nickel under diverse conditions using molecular dynamics simulations. In particular, the effects of solute hydrogen concentrations, cascade energies, and temperatures are explored. The results show a pronounced correlation between these defects and hydrogen atoms, which form clusters with varying hydrogen concentrations. With increasing the energy of a primary knock-on atom (PKA), the number of surviving self-interstitial atoms (SIAs) also increases. Notably, at low PKA energies, solute hydrogen atoms impede the clustering and formation of SIAs, while at high energies, they promote such clustering. The impact of low simulation temperatures on defects and hydrogen clustering is relatively minor. High temperature has a more obvious effect on the formation of clusters. This atomistic investigation offers valuable insights into the interaction between hydrogen and defects in irradiated environments, thereby informing material design considerations for next-generation nuclear reactors.

Influence of Pre-Pressing Ring on the Weld Quality of Ultrasonically Welded Short Carbon Fiber Reinforced Nylon 6 Composite.

The ultrasonic welding (UW) technique is a fast-joining process; it is very suitable for the carbon fiber reinforced thermoplastic (CFRTP) composite. For improving the consistency of the welded joint quality, a new pre-pressing ring clamp (PPRC) was designed for ultrasonic welding carbon fiber reinforced nylon composites in this paper. The effects of the PPRC on the weld quality of the ultrasonic welding welded 4.0 mm thick 30% mass short carbon fiber reinforced Nylon 6 composite was investigated and compared with that of normal clamp weld joint. The weld strength, microstructure, and temperature evolution of the joint were analyzed by tensile test, scanning electron microscope, and temperature measurement. The results showed that the PPCR UW joints had larger central weld nugget size (478 mm2 vs. 300 mm2), thicker stable fusion region thickness (1.10 mm vs. 0.96 mm), resulting in a higher joint strength (6.86 kN vs. 6.21 kN) compared with the normal clamp UW joints under the same welding parameters. The real-time monitor curve of the horn displacement and temperature at the faying interface showed that the PPRC increased the heat rating at the faying interface during instable melting stage. The PPRC could improve the contact condition between workpieces and the utilization efficiency of ultrasonic energy, which boosted the melting rate of materials at faying interface and consequently the formation of a sound joint with enough weld size (i.e., 433 mm2) in a shorter welding time (i.e., 1.3 s). Therefore, the flexibility of component assembly would be increased by the use of this sort of clamps.

Effect of Preload on the Weld Quality of Ultrasonic Welded Carbon-Fiber-Reinforced Nylon 6 Composite.

Ultrasonic welding (UW) of polymeric composites is significant in automobile industry; however, maintaining the perfect contact condition between workpieces is a great concern. In this study, effect of preloading and welding pressure on strengths of UWed 2.3-mm-thick short carbon fiber reinforced nylon6 (Cf/PA6) joints with poor contact between workpieces was investigated through stress simulation and energy dissipation at the faying interface. Results showed the application of preloading can increase the strength of normal joint by 18.7% under optimal welding parameters. Gaps between upper and lower workpieces decreased the joint strength significantly, especially for gaps greater than 1.5 mm. Preloading improved the strengths of the joints with gaps remarkably, where the strength of joints with 1.5 mm gap recovered to 95.5% of that the normal joint. When combining the weld nugget evolution, stress-deformation simulation during UW, and ultrasonic vibration transmission analysis, the improvement mechanism of the joint under preloading was mainly because the preloading compacted the contact between workpieces, which favored the energy transmission at faying interface.

Influence of ball milling process on microstructure, mechanical and thermal expansion properties of ZrMgMo3O12/Al-40Si composites.

In this study, ZrMgMo3O12/Al-40Si (ZMMO/Al-40Si) composites with 15 wt% ZrMgMo3O12 were fabricated by ball milling-vacuum hot pressing (VHP) processes. The effect of ball milling processes on the microstructure, compressive properties and coefficient of thermal expansion (CTE) of the composites were investigated. It is found that ball milling treatments of mixed ZMMO/Al-40Si powders refine the particles of ZMMO reinforcements and primary Si in ZMMO/Al-40Si composites and improve the distribution of ZMMO reinforcements in α-Al matrix, resulting in the increase of the compressive strength and the decrease of the CTE of ZMMO/Al-40Si composites. The highest compressive yield strength of 430.82 MPa and the lowest CTEs of 5.8 × 10-6/°C (RT - 400 °C) are obtained after ball milling for 8 h at 250 rpm, increasing by 145.9% and decreasing by 61.3% respectively compared with the compressive yield strength and CTE of Al-40Si alloy. Among the reinforcements commonly used in aluminum matrix composites, ZMMO reinforcement has the highest reduction efficiency for CTE of ZMMO/Al-40Si composite. The application of high-energy ball milling to refine the microstructure is a promising method that can simultaneously increase the strength and reduce the CTEs of ZMMO/Al-40Si composites.

Double-Pulse Ultrasonic Welding of Carbon-Fiber-Reinforced Polyamide 66 Composite.

Ultrasonic welding of thermoplastics is widely applied in automobile and aerospace industries. Increasing the weld area and avoiding thermal decomposition are contradictory factors in improving strength of ultrasonically welded polymers. In this study, relations among the loss modulus of carbon-fiber-reinforced polyamide 66 composite (CF/PA 66), time for obtaining stable weld area, and time for CF/PA 66 decomposition are investigated systematically. Then, a double-pulse ultrasonic welding process (DPUW) is proposed, and the temperature evolutions, morphologies and structures of fractured surfaces, and tensile and fatigue properties of the DPUWed joints are measured and assessed. Experimental results show the optimal welding parameters for DPUW include a weld time of 2.1 s for the first pulse, a cooling time of 12 s, and a weld time of 1.5 s for the second pulse. The DPUW process enlarged the weld area while avoided decomposition of CF/PA 66 under appropriate welding parameters. Compared to the single-pulse welded joint, the peak load, weld area, and endurance limit of the DPUWed joint increased by about 15%, 23% and 59%, respectively. DPUW also decreases the variance in strengths of the joints.

Effect of ball milling process on the mechanical and thermal properties of the nanodiamond/2024Al composites.

In this study, 5 wt.% nanodiamond (ND) reinforced 2024Al matrix composites (ND/2024Al) were fabricated with various ball milling processes. The microstructure, compressive yield strength (σyc) and coefficient of thermal expansion (CTE) of ND/2024Al composites were investigated. It is found that the addition of 5 wt.% NDs significantly increases the σyc and decreases the CTE of 2024Al. High energy ball milling further increases σyc and decreases CTEs of ND/2024Al composite due to it enhances the fine grain strengthening of α-Al matrix and the dispersion strengthening of NDs, decreases the thermal mismatch stress at the ND/α-Al matrix interface, and increases the constraint of NDs on α-Al. The composites fabricated by the combinations of ball milling speeds and times of (5-7) h×(200-250)rpm and 9 h×300 rpm have the highest σyc and the lowest CTE respectively. Considering the different influence of ball milling parameters on σyc and CTEs, a evaluation coefficient α=σycC⋅εkcCσycM⋅εkcM⋅CTEMCTEC is proposed to evaluate the synergistic influence of mechanical properties and CTEs on the dimensional stability of ND/2024Al composites. Large value of α may lead to high dimensional stability of material, hence the α can be used to determine the ball milling parameters.The ball milling process of 250-300 rpm ball milling speeds and 5-7 h ball milling times are recommended based on α, which causes a 95-100 % increase in σyc and a 30-35 % decrease in CTE compared with 2024Al alloy, respectively.

Effect of pre-strain on microstructure and micro-yield properties of Al-Cu-Li alloy.

In this study, Al-Cu-Li alloys were pre-strained to various plastic strains before ageing. The T1 (Al2CuLi) precipitates and dislocation density in various pre-strained Al-Cu-Li alloys were analyzed with transmission electron microscopy (TEM) and X-ray diffraction (XRD) technology respectively. The micro-yield strength (Micro-YS) of tested alloys was measured and the strengthening mechanism was discussed. It is found that the pre-strain increases the dislocation density, promotes the precipitation and inhibits the growth of T1 precipitates. The precipitation strengthening of T1 precipitates is higher than strain strghening of dislocations and it first increase then decrease whearas the strain strenthening continuously increase with pre-strain. The improvement in strength of Al-Cu-Li alloy caused by pre-straining is mainly due to strain strengthening rather than precipitation strengthening. Therefore, although pre-strain improves the macro-yield strength (Macro-YS) as well as the Micro-YS, excessive pre-strains are not conducive to the improvement of the Micro-YS. The pre-strain of 2% is a promising method to simultaneously improve the Micro-YS and Macro-YS of Al-Cu-Li alloys due to its synergistic improvement effect on precipitation strengthening and strain strengthening. Macro-YS and Micro-YS of pre-strained Al-Cu-Li alloys can be estimated with a simple strength mode. However, the larger error between the estimated and measured Micro-YS suggests that the accurate estimation of Micro-YS requires further to consider the adverse effect of mobile dislocations caused by pre-strain on the Micro-YS.

Effect of Zr content on microstructure and mechanical properties of lightweight Al2NbTi3V2Zrx high entropy alloy.

Lightweight Al2NbTi3V2Zrx (x = 1.0, 0.8, 0.6, 0.4, 0.2, 0) high entropy alloys are produced by mechanical milling and vacuum hot pressing. The microstructure, phase evolution and mechanical properties of the alloys are analyzed. The microstructure of the alloys with x = 1.0, 0.8, 0.6 consists of BCC solid solution matrix and two intermetallics (i.e., α and ß), and then ß phase disappears in Al2NbTi3V2Zr0.4 alloy. Further decreasing Zr content to below 0.2, α phase vanishes and γ and δ intermetallics emerge in Al2NbTi3V2Zr0.2 and Al2NbTi3V2 alloys. The Al2NbTi3V2Zrx alloys cannot obtain a single phase structure by decreasing Zr content with current fabrication process, which is likely because that the mixing entropy of the HEA system is not large enough to prohibit the formation of the secondary phases at hot pressing temperature of 1250 °C. All the bulks possess low density ranging from 4.93 to 5.21 g/cm3. Hardness of the Al2NbTi3V2Zrx alloys decreases from 781 HV to 697 HV and then increases to 814 HV with the decrease of Zr from x = 1 to 0. This varying tendency is closely related with the content of secondary intermetallic phases. The compressive test shows the Al2NbTi3V2Zr0.4 alloy has a yield strength of 1742 MPa, fracture strength of 2420 MPa, compressive strain of 38.2 %, which is probably related to its simplest microstructure. The comprehensive mechanical property of Al2NbTi3V2Zr0.4 alloy is superior to the majority of other HEAs and Ti64 alloy.

Effect of external stress on the microstructure and mechanical properties of creep-aged Al-Cu-Li-Ag alloy.

The effects of external stress on the precipitation of T1 precipitates and mechanical properties of creep-aged Al-Cu-Li-Ag alloys are investigated. Promotion mechanisms of external stress to the precipitation of T1 precipitates are discussed. It is found that external stress significantly promotes the precipitation and improves the distribution of the T1 precipitates in the creep-aged alloys. There is a threshold stress, close to the yield stress, that has only a limited promotion effect on the precipitation of T1 precipitates. The external stress below and above the threshold stress promotes the precipitation of T1 precipitates by two different mechanisms. One is the promotion mechanism of lattice distortion produced by the elastic stress. Another is the promotion mechanism of multiplication of dislocations produced by the plastic stress. Both elastic and plastic external stress can synergistically improve the strength and ductility. Especially, the plastic external stress resulted in the best improvement to ductility of creep-aged alloys. Hence, the creep ageing with plastic external stress is an alternative method to synergistically improve the strength and ductility of Al-Cu-Li-Ag alloys. However, it is necessary to avoid using excessive plastic stress for the creep ageing because it may cause creep damage and degrade its mechanical properties.

Effect of Co on the microstructure and oxidation behavior of CoxCrCuFeMnNi high entropy alloy powders.

The microstructure, phase, alloying behavior, and oxidation behavior of the CoxCrCuFeMnNi (x = 0, 0.5, 1.0, 1.5, 2.0, named as Co0, Co0.5, Co1.0, Co1.5, and Co0.5, respectively) high entropy alloy powders (HEAPs) prepared by mechanical alloying were studied. The results indicated that the HEAPs began to be alloyed after ball milling for 5 h, and the particle size is about 40∼60 µm. After 50 h of milling, the Co0 and Co0.5 HEAPs are composed of metastable FCC and minor BCC solid solution phases, while the other HEAPs consist of single metastable FCC solid solution phase. After vacuum annealing or atmospheric oxidation at 700 °C, the metastable FCC and BCC phases decompose into FCC1 and FCC2 and ρ phases, respectively. The oxidation mass gain of CoxCrCuFeMnNi HEAPs shows a parabolic upward trend. With the increase of Co content, the oxidation rate constant decreases, indicating that the oxidation resistance of the HEAPs decreases with the increase of Co content.

Immunohistochemical detection of islet-1 and neuronal nitric oxide synthase in the dorsal root ganglia (DRG) of sheep fetuses during gestation.

This study first investigated the ontogeny of Islet-1 and neuronal nitric oxide synthase (nNOS) expression and their co-localization in the DRG of sheep fetuses during gestation by immunohistochemistry (IHC). The results showed that Islet-1 and nNOS were located in the nuclei and cytoplasm of DRG neurons, respectively. The relative percentages of Islet-1-immunopositive (Islet-1(+)) neurons accounting for the total DRG neurons were 90%, 79%, 66%, and 53% at days 60, 90, and 120 of gestation and postnatally, respectively. The percentage of nNOS-immunopositive (nNOS(+)) neurons was 94% at day 60 and declined to approximately 30% at day 90, with no obvious further change until the postnatal period. Dual IHC showed that approximately 69% Islet-1(+) neurons express nNOS at day 60 of gestation. This proportion declined to approximately 24% at day 90, after which there was no significant change until birth. We also observed that most Islet-1(+) and nNOS(+) neurons belonged to small and medium-sized DRG neurons from day 90 of gestation to the postnatal period. These results suggest that both Islet-1 and nNOS are important for the differentiation and maintenance of some specific phenotypes of DRG neurons during late gestation of sheep fetuses, although the related mechanisms need to be further elucidated.