Tribological Behaviors of Electroless Nickel-Boron Coating on Titanium Alloy Surface

Titanium alloys are excellent structural materials in engineering fields,but their poor tribological properties limit their further applications.Electroless plating is an effective method to enhance the tribological performance of alloys,but it is difficult to efficiently apply to titanium alloys,due to titanium alloy’s strong chemical activity.In this work,the electroless Nickel-Boron(Ni-B)coating was successfully deposited on the surface of titanium alloy(Ti-6AL-4V)via a new pre-treatment process.Then,linearly reciprocating sliding wear tests were performed to evaluate the tribological behaviors of titanium alloy and its electroless Ni-B coatings.It was found that the Ni-B coatings can decrease the wear rate of the titanium alloy from 19.89×10^(−3)mm^(3)to 0.41×10^(−3)mm^(3),which attributes to the much higher hardness of Ni-B coatings.After heat treatment,the hardness of Ni-B coating further increases corresponding to coating crystallization and hard phase formation.However,heat treatment does not improve the tribological performance of Ni-B coating,due to the fact that higher brittleness and more severe oxidative wear exacerbate the damage of heat-treated coatings.Furthermore,the Ni-B coatings heat-treated both in air and nitrogen almost present the same tribological performance.The finding of this work on electroless coating would further extend the practical applications of titanium alloys in the engineering fields.

Laser machining fundamentals:micro,nano,atomic and close-to-atomic scales

With the rapid development in advanced industries,such as microelectronics and optics sectors,the functional feature size of devises/components has been decreasing from micro to nanometric,and even ACS for higher performance,smaller volume and lower energy consumption.By this time,a great many quantum structures are proposed,with not only an extreme scale of several or even single atom,but also a nearly ideal lattice structure with no material defect.It is almost no doubt that such structures play critical role in the next generation products,which shows an urgent demand for the ACSM.Laser machining is one of the most important approaches widely used in engineering and scientific research.It is high-efficient and applicable for most kinds of materials.Moreover,the processing scale covers a huge range from millimeters to nanometers,and has already touched the atomic level.Laser–material interaction mechanism,as the foundation of laser machining,determines the machining accuracy and surface quality.It becomes much more sophisticated and dominant with a decrease in processing scale,which is systematically reviewed in this article.In general,the mechanisms of laser-induced material removal are classified into ablation,CE and atomic desorption,with a decrease in the scale from above microns to angstroms.The effects of processing parameters on both fundamental material response and machined surface quality are discussed,as well as theoretical methods to simulate and understand the underlying mechanisms.Examples at nanometric to atomic scale are provided,which demonstrate the capability of laser machining in achieving the ultimate precision and becoming a promising approach to ACSM.

High-Performance Aqueous Zinc-Ion Battery Based on Laser-Induced Graphene

Zn-ion batteries(ZIBs)have a broad application prospect because of their advantages of high power,large capacity,and high energy density.However,the development of high-capacity,long-lifespan ZIBs is challenging because of the faster dendrite growth and the occurrence of the hydrogen evolution reaction.Laser-induced graphene(LIG)is a material with many defects and heteroatoms.Because of these characteristics,it plays an important role in improving nucleation.A simple and effective method for preparing LIG was proposed in this paper,and the LIG was covered on the surface of Zn foil to form a composite structure.This structure substantially reduces the nucleation overpotential of Zn and slows down the dendrite growth of Zn by improving the nucleation behavior of Zn^(2+).Simultaneously,the three-dimensional porous structure increases the specific surface area of the electrode,so the battery has a larger specific capacity.Compared with the bare Zn electrode,the composite electrode possesses lower overpotential and longer cycle life.In addition,the full battery using activated carbon as the active material exhibits great rate and cycle performance.This facile and scalable approach may solve the problem of Zn dendrite growth,which is crucial for the large-scale application of ZIBs.

Quantitative analysis of the tribological properties of phosphate glass at the nano- and macro-scales

Processing(grinding,polishing)of phosphate laser(PL)glass involves material removal at two vastly different(spatial)scales.In this study,the nano‐and macro‐tribological properties of PL glass are investigated by rubbing the glass against a SiO_(2) counter‐surface in both dry and humid conditions.The results indicate that the friction of the PL glass/SiO_(2) pair has opposing trends at the nano‐and macroscales.At the nanoscale,the friction coefficient(COF)in humid air is much higher than in dry air,which is attributed to the capillary effect of the absorbed water‐film at the interface.At the macroscale,on the other hand,the COF in humid air is lower than in dry air,because the water‐related mechanochemical wear makes the worn surface less susceptible to cracking.Material removal for PL glass is better facilitated by humid air than by dry air at both scales,because the stress‐enhanced hydrolysis accelerates the material‐removal process in glass.Moreover,the material‐removal is more sensitive to contact pressure at the macroscale,because stronger mechanical‐interaction occurs during material removal at the macroscale with the multi asperity contact mode.At the macroscale,the material removal is more sensitive to contact pressure in humid air compared to dry air.Because almost all mechanical energy is used to remove material in humid air,and most of the mechanical energy is used to produce cracks in PL glass in dry air.The results of this study can help optimize the multi‐scale surface processing of optical glasses.

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.