Mussel-inspired PTW@PDA composites for developing high-energy gun propellants with reduced erosion and enhanced mechanical strength

The severe erosion and inadequate mechanical strength are prominent challenges for high-energy gun propellants.To address it,novel PTW@PDA composites was prepared by polydopamine(PDA)-modifying onto potassium titanate whisker(PTW,K_(2)Ti_(6)O_(13)),and after was incorporated into gun propellant as erosion-reducing and mechanical-reinforcing fillers.The interfacial characterizations results indicated that as-prepared PTW@PDA composites exhibits an enhanced surface compatible with propellant matrix,thereby facilitating their dispersion into propellants more effectively than raw PTW materials.Compared to original propellants,PTW@PDA-modified propellants exhibited significant less erosion,with a Ti-Kbased protective coating being detected on the eroded steel.And 0.5 wt%and 1.0 wt%addition of PTW@PDA significantly improved impact,compressive and tensile strength of propellants.Despite the inevitably reduction in relative force,PTW@PDA slightly increase propellant burning rate while exerting little adverse impact on propellant dynamic activity.This strategy can provide a promising alternative to develop high-energy gun propellant with less erosion and more mechanical strength.

An efficient method to engage oxide ceramics in low-temperature interfacial reactions: Microstructure evolution and kinetics behaviors based on supercooling in a transient liquid phase bonding joint

Ductile transient liquid phase(TLP)bonding joints reinforced by multiple precipitates were produced using novel pre-sintered coatings and Au-Si fillers;therefore,the highest strength of NiTi/sapphire joints brazed at 460℃ for 30 min reached 72 MPa.The pre-sintering process improved the surface-active of sapphire by forming metastable Ti_(3)O and non-stoichiometric Al_(2)O_(3).The typical brazing seam consisted of O-rich compounds,TiSi_(2),and Ti-Ni-Si,wherein the O-rich phase featured different crystallinity depending on the oxygen content.The sapphire/seam interface was either a nanoscale diffusion region or a Si-rich amorphous layer.The breakdown of the Stokes-Einstein relation(SER)occurred,and the deviation from SER increased with a higher cooling rate.The influence of coating thickness was reflected in(i)the supercooling related to the viscosity and fractional exponent of liquids and(ii)the microstructural change of the joint related to the driving force for crystal growth.This work presented a new strategy for joining ceramics to metals at lower temperatures but using the joint at higher temperatures;furthermore,gave an insight into the microstructure evolution and kinetics behaviors based on supercooling in a transient liquid phase bonding joint.

Tribological properties of polyimide composites reinforced with fibers rubbing against Al_(2)O_(3)

Reinforcing fillers are of great importance in tribological performance and tribofilm formation of polymeric composites.In this study,the tribological properties of aramid particle(AP)and short carbon fiber(SCF)reinforced polyimide(PI)composites were added to hexagonal boron nitride(h-BN),and silica(SiO_(2))nanoparticles sliding against alumina were comprehensively investigated.When sliding occurred with AP-reinforced PI composites,the tribological properties were not closely depended on the pressure×velocity(p×v)factors and the nanoparticles.The interactions between AP and its counterpart could not induce tribo-sintering of the transferred wear debris.As such,the tribofilm seemed to be in a viscous state,leading to higher friction and wear.However,the inclusion of hard SCF into the PI matrix changed the interfacial interactions with alumina.A robust tribofilm consisting of a high fraction of silica was generated when the SCF-reinforced PI was added to the SiO_(2) nanoparticles.It exhibited a high load-carrying capability and was easily sheared.This caused a significant decrease in the friction and wear of the PI composite at 8 MPa·1m/s.Moreover,due to their high melting point,few h-BN nanoparticles were observed in the tribofilm of the SCF-reinforced PI when hexagonal boron nitride was added.