High-temperature Thermal Properties and Wear Behavior of Basalt as Heat Storage Material for Concentrated Solar Power Plants

The microstructures,components,thermal stability,specific heat capacity and thermal conductivity of basalt sample were studied.Besides,as a comprehensive result of thermal expansion and contraction process,both the friction coefficient and wear rate of the basalt sample were also characterized.Our results indicate that basalt is an excellent candidate to be used as thermal energy storage material for concentrated solar power plants,and also provide a strategy for solar energy utilization in volcanic area with excellent geographical environment.

Influence of quenching medium on the dendrite morphology,hardness,and tribological behaviour of cast Cu-Ni-Sn spinodal alloy for defence application

Cu-Ni-Sn spinodal alloys(Spinodal bronze)are potential materials with robust applications in components associated with defence applications like bearings,propellers,bushes,and shafts of heavily loaded aircraft,off-road vehicles,and warships.This paper presents a comparative study using water,Brine solution,and SAE 40 oil as the quenching media in regular bronze(Cu-6Sn)and spinodal bronze(Cu-9Ni-6Sn)alloys.Morphological analysis was conducted by optical microscopy,transmission electron microscopy(TEM),and X-ray diffraction technique(XRD)on bronze and spinodal bronze samples immersed in the three different quenching media to understand the grain size and hardness values better.Tribological analysis was performed to analyze the effect of quenching media on the wear aspects of bronze and spinodal bronze samples.The hardness value of the brine-aged spinodal bronze samples was as high as 320 Hv,and the grain size was very low in the range of 60μm.A quantitative comparison between brine-aged regular bronze and brine-aged spinodal bronze showed that the hardness(Hv)was almost 80%higher for brine-aged spinodal bronze.Further,the grain size was approximately 30%finer for spinodal bronze when compared with regular bronze.When the load was increased in spinodal bronze samples,there was an initial dip in wear rate followed by a marginal increase.There was a steady increase in friction coefficient with a rise in load for brine-aged regular bronze and spinodal bronze samples.These results indicate that brine solution is the most effective quenching medium for cast Cu-Ni-Sn spinodal alloys.

Insights into the oxidation resistance mechanism and tribological behaviors of multilayered TiSiN/CrVxN hard coatings

In the last decades,vanadium alloyed coatings have been introduced as potential candidates for self-lubrication due to their perfect tribological properties.In this work,the influence of V incorporation on the wear performance and oxidation resistance of TiSiN/CrN film coatings deposited by direct current(DC)reactive magnetron sputtering is investigated.The results show that vanadium incorporation significantly decreases the oxidation resistance of the coatings.In general,two layers are formed during the oxidation process:i)Ti(V)O_(2) on top,followed by a protective layer,which is subdivided into two layers,Cr_(2)O_(3) and Si-O.ii)The diffusion of V controls the oxidation of V-containing coatings.The addition of vanadium improves the wear resistance of coatings,and the wear rate decreases with increasing V content in the coatings;however,the friction coefficient is independent of the chemical composition of the coatings.The wear of the V-containing coatings is driven by polishing wear.

Improving energy utilization efficiency of electrical discharge milling in titanium alloys machining

Electrical discharge milling(ED-milling) can be a good choice for titanium alloys machining and it was proven that its machining efficiency can be improved to compete with mechanical cutting. In order to improve energy utilization efficiency of ED-milling process, unstable arc discharge and stable arc discharge combined with normal discharge were implemented for material removal by adjusting servo control strategy. The influence of electrode rotating speed and dielectric flushing pressure on machining performance was investigated by experiments. It was found that the rotating of electrode could move the position of discharge plasma channel, and high pressure flushing could wash melted debris out the discharge gap effectively. Both electrode rotating motion and high pressure flushing are contributed to the improvement of machining efficiency.

Dry sliding wear behavior of an extruded Mg-Dy-Zn alloy with long period stacking ordered phase

The dry sliding wear behavior of extruded Mg-2Dy-0.5Zn alloy(at.%)was investigated using a pin-on-disk configuration.The friction coefficient and wear rate were measured within a load range 20-760 N at a sliding velocity of 0.785 m/s.Microstructure and wear surface of alloy were examined using scanning electron microscopy.The mechanical properties of alloy were tested at room and elevated temperatures.Five wear mechanisms,namely abrasion,oxidation,delamination,thermal softening and melting dominated the whole wear behavior with increasing applied load.The extruded Mg-2Dy-0.5Zn alloy exhibited the better wear resistance as compared with as-cast Mg_(97)Zn_(1)Y_(2) alloy under the given conditions through contact surface temperature analysis.The improved wear resistance was mainly related to fine grain size,good thermal stability of long period stacking order(LPSO)phase and excellent higher-temperature mechanical properties.

Microstructural evolution of die-cast and homogenized AZ91 Mg-alloys during dry sliding condition

Received 16 July 2016;revised 24 January 2017;accepted 7 February 2017 Available online 22 February 2017 Abstract Microstructural evolution of die-cast and homogenized AZ91 Mg-alloys was investigated during dry sliding wear condition.Tribological tests were performed using a pin-on-disc(EN8 steel)configuration with a normal load of 50 N at a constant sliding speed of 2.5 ms^(−1) under ambient environment.Delamination was recognized as a predominant wear mechanism in both of these materials.The die-cast AZ91 Mg-alloy exhibits lower coefficient of friction and higher wear rate.This can be ascribed to increase in the intensity of load bearing capacity of hardβ-Mg_(17)Al_(12) phase,and crack formation/de-cohesion at the interface between primaryα-Mg and discontinuousβ-Mg_(17)Al_(12) phases.On the contrary,the homogenized AZ91 Mg-alloy experiences higher coefficient of friction and lower wear rate.The friction-induced microstructural evolution(supersaturatedα-Mg to eutectic(α+β-Mg_(17)Al_(12)))tending to minimize the wear rate by providing barrier to material removal in the near surface region of homogenized AZ91 Mg-alloy.Therefore,experimental observation revealed that an inverse relationship exists between wear rate and coefficient of friction for the investigated materials.The analysis of worn surfaces and subsurfaces by electron microscopy provided evidence to delamination wear and microstructural evolution.

Correlation between test temperature, applied load and wear transition of Mg97Zn1Y2 alloy

Dry sliding wear tests were performed on Mg97 Zn1 Y2 alloy at various temperatures of 20,50,100,150 and 200°C using a pin-on-disc wear testing machine in order to reveal mild-severe(M-S)wear transition mechanism during elevated-temperature wear testing.It was shown that at each test temperature,the wear rate increased with increasing load,and all wear rate-load curves demonstrated two distinct stages i.e.mild and severe wear stages.The predominant wear mechanisms operating in mild and severe wear stages were analyzed,and they were indicated in the mild and severe wear regimes of a wear mechanism transition map,respectively.M-S wear transition mechanism was analyzed by comparison of microstructure transformation and hardness change in subsurfaces of samples tested in mild and severe wear stages,from which M-S wear transition mechanism was confirmed as softening of surface material arising from dynamic recrystallization(DRX)microstructure transformation.The M-S wear transition load was found to have a linear relationship with test temperature,and decreased with rising test temperature.M-S wear transition obeyed a critical surface DRX temperature(SDT)criterion under given conditions,and the transition loads were estimated at various test temperatures by using the criterion.

Structure and Tribological Properties of CrTiAlN Coatings Deposited by Multi-Arc Ion Plating

CrTiAIN coatings were prepared by using a home-made industrial scale multi-arc ion plating system. The coatings were found to be composites of face-center-cubic CrN and TiN. The surface roughness, microhardness, and tribological properties of the films were significantly affected by the nitrogen pressure and dc-pulsed bias voltage applied to the substrate. The CrTiA1N coatings with the smoothest surfaces were obtained at optimum conditions of nitrogen pressure of 5.0 Pa and bias voltage of -200 V. The samples were found to exhibit a hardness of 2900 HV0.05 with an average friction coefficient of 0.16 and wear rate of 1.5× 10^-16 m^3/N.m against cemented carbide.

Analysis of Wear Mechanism and Influence Factors of Drum Segment of Hot Rolling Coiler

Because the work environment of segment is complex, and the wear failures usually happen, the wear mechanism corresponding to the load is a key factor for the solution of this problem. At present, many researchers have investigated the failure of segment, but have not taken into account the compositive influences of matching and coiling process. To investigate the wear failure of the drum segment of the hot rolling coiler, the MMU-5G abrasion tester is applied to simulate the wear behavior under different temperatures, different loads and different stages, and the friction coefficients and wear rates are acquired. Scanning electron microscopy（SEM） is used to observe the micro-morphology of worn surface, X-ray energy dispersive spectroscopy（EDS） is used to analyze the chemical composition of worn surface, finally the wear mechanism of segment in working process is judged and the influence regulars of the environmental factors on the material wear behaviors are found. The test and analysis results show that under certain load, the wear of the segment changes into oxidation wear from abrasive wear step by step with the temperature increases, and the wear degree reduces; under certain temperature, the main wear mechanism of segment changes into spalling wear from abrasive wear with the load increases, and the wear degree slightly increases. The proposed research provides a theoretical foundation and a practical reference for optimizing the wear behavior and extending the working life of segment.

Effect of Spraying Parameters on Deposition Efficiency and Wear Behavior of Plasma Sprayed Alumina-Titania Composite Coatings

The effects of parameters, in the process of plasma-sprayed ceramic coating, upon the deposition efficiency of alumina-13 wt.% titania composite coatings are reported. The coatings were prepared by the atmospheric plasma spray process. The plasma torch input power, flow rates of primary, secondary and carrier gas, powder feed rate and spraying distance were considered as variables. The results show that the variations in all the selected spraying parameters strongly affect the deposition efficiency. The micro-hardness, as well as erosive and sliding wear rates of the coating are also affected by these parameters. Especially the input power strongly affects the phase and microstructure of the coatings.

Synthesis and Tribological Properties of Copper-alumina Nanocomposites Prepared by Coprecipitation Technique

The objective of this work is to study the synthesis of copper-alumina nanocomposites using the coprecipitation process and hot-pressing method, and investigate their mechanical properties. The effects of calcination temperature on the average size of composite particles and chemical composition after calcination were also analyzed. The sintering parameters including sintering temperature, hot pressure and packing time were optimized to fabricate the alumina nanoparticles reinforced copper matrix composites（CMCs）. The density, microhardness and tribological properties of the CMCs reinforced with 1 wt%, 2 wt%, 3 wt%, 4 wt% and 5 wt% of alumina nanoparticles were investigated correspondingly. The results showed that the optimum preparation parameters for the CMCs were 900 ℃ of hot pressing temperature, 27.5 MPa of hot pressure and 2 hrs of packing time. The CMC reinforced with 2 wt% of alumina nanoparticles had the lowest wear rate, with the relative wear resistance of 3.13.

Impact wear properties of dissimilar joints between bainitic frogs and pearlite rails

The impact wear behavior and damage mechanism of dissimilar welded joints between U26Mn frog and U75 V rail before and after normalizing treatment were studied by cyclic impact tests.The experiment indicated that the impact wear volume of the joints increased with the increasing number of impact cycles.The main wear mechanisms include pitting wear,mild fatigue wear,delamination wear,and fatigue wear,and plastic deformation was the primary impact wear mechanism.Among them,fatigue wear had the greatest influence on wear volume,while other wear mechanisms had limited effect.The impact wear resistance of the base material was better than that of the heat-affected zone.Normalizing treatment was beneficial to improving the impact wear resistance of welded joints owing to its effect to promote pearlite recovery,grain refinement,and uniform distribution of grains.The martensite generated in the rail welded joints aggravated the impact wear damage to the materials,which should be avoided.

Measurement of bit-rock interface temperature and wear rate of the tungsten carbide drill bit during rotary drilling

Rock drilling is an essential operation in mining industries.Temperature at the bit-rock interface plays a major role in the wear rate of the drill bit.This paper primarily focuses on the wear rate of tungsten carbide(WC)drill bit and the interrelationship between temperature and wear rate during rotary drilling operations conducted using a computer numerical control(CNC)machine.The interrelationship between the temperature and wear rate was studied with regard to three types of rock samples,i.e.,fine-grained sandstone(FG)of uniaxial compressive strength(UCS)that is 17.83 MPa,medium-grained sandstone(MG)of UCS that is 13.70 MPa,and fine-grained sandstone pink(FGP)of UCS that is 51.67 MPa.Wear rate of the drill bit has been measured using controlled parameters,i.e.,drill bit diameter(6,8,10,12,and 16 mm),spindle speed(250,300,350,400,and 450 rpm),and penetration rate(2,4,6,8,and 10 mm/min),respectively.Further,a fully instrumented laboratory drilling set-up was utilized.The weight of each bit was measured after the bit reached 30 mm depth in each type of the rock sample.Furthermore,effects of the bit-rock interface temperature and operational parameters on wear rate of the drill bits were examined.The results show that the wear rate of drill bits increased with an increase in temperature for all the bit-rock combinations considered.This is due to the silica content of the rock sample,which leads to an increase in the frictional heat between the bit-rock interfaces.However,in case of medium-grained sandstone,the weight percentage(wt%)of SiO2 is around 7.23 wt%,which presents a very low wear rate coefficient of 6.33×10^–2 mg/(N?m).Moreover,the temperature rise during drilling is also minimum,i.e.,around 74℃,in comparison to that of fine-grained sandstone and fine-grained sandstone pink.In addition,this paper develops the relationship between temperature and wear rate characteristics by employing simple linear regression analysis.

Probabilistic model of disc-cutter wear in TBM construction:A case study of Chaoer to Xiliao water conveyance tunnel in China

Disc-cutters play a crucial role in the penetration process during construction using a tunnel boring machine(TBM).Their wear status has a significant impact on working efficiency and costs that accounts for a large part of the budget.Discovering the wear pattern and characteristics of disc-cutters could provide a valuable guide for field maintenance and cutter replacement work.It also provides insight into the wear mechanism of cutters at different positions for optimizing the disc-cutter arrangement design.In this study,the cutter wears data of 34 disc-cutters over 643 days in the Chaoer River to Xiliao River water diversion tunnel was collected.The dataset contains 21862 manual readings measured from 1079 disc-cutters replaced in this project.The raw data from the hard copy version was transformed into a digital twin database by eliminating abnormal data,filling in empty values,and performing linear interpolations.It has been found that the cutters can pass statistical testing for an exponential probability distribution function with respect to the wear rate(w).The regression ratios of R2are essentially greater than 0.8.These findings would help estimate the future service life of a currently working cutter,which means significant savings for the costly disccutters.The application of exponential distribution has the advantage of only one shape parameter,λ,whose reciprocal represents both the statistical mean and standard deviation of the wear rates.It is simple and practically amenable.A preliminary study was carried out to simulate the wear process between two neighboring cutters for drafting a replacement plan for disc-cutters by the Monte Carlo method.The prediction results agreed reasonably well with the measured information.

Tribological behavior of shape memory cyanate ester materials and their tunable friction mechanism

High-performance polymer friction materials with tunable tribological behavior to fit varied work conditions remain a challenge of widespread interest for a variety of applications.Shape memory polymer exhibits morphing and modulus changing over temperature changing provides a promising material to adjust the friction process.Herein,we investigated the tribological properties of shape memory cyanate ester(SMCE)under different conditions.The SMCE exhibits the tribological behavior of good friction material with stable high coefficient of friction(COF)and a low wear rate.Besides,the COF increases and wear rate decreases with the temperature increasing show the tunable friction property of the SMCE.We propose a new model of wear-compensation through shape recovery to explain the adjustable friction behavior of thermal-responsive polymer from the aspect of shape recovery and energy conversion.This study provides a high-performance friction material and paves the route for the application of shape memory polymer(SMP)in tribology field with tunable property.

Tribological and mechanical behaviours of resin-based friction materials based on microcrack filling

To enhance the friction performance of resin-based friction materials,five types of specimens with different polymer ether ketone(PEEK)contents were fabricated and their physiomechanical behaviours were tested and,their tribological properties were investigated using a JF150F-II constant-speed tester.It was found that the addition of PEEK had a positive influence on the properties of the friction materials,and sample FM-3(the shorthand of‘Friction Materials-3’,containing 2 wt%PEEK)exhibited improved friction performance with a fade ratio and recovery ratio of 8.6%and 101.1%respectively.Among all samples,FM-4(the shorthand of‘Friction Materials-4’,con-taining 3 wt%PEEK)had the lowest specific wear rate with a value of 0.622×10^(−7)cm^(3)(N⋅m)^(−1)at 350℃.The PEEK can fill the microcracks in the composite at a high tem-perature and can also cover the hard abrasive particles to prevent them from directly damaging the composite.The findings from this study afford a foundation for studies to further improve the properties of resin-based friction materials.

Laser cladding of high-entropy alloy on H13 steel

High-entropy alloy layer up to 150 lm in thickness was formed on H13 substrate with a metallurgical bonding at the coating/substrate interface. Simple solid solution phases were formed in the coating layer with a typical microstructure composed of both dendrite and interdendrite. The microstructure at the top of the cladding zone consists of equiaxed grains while that at the bottom consists of columnar grains. The coating layer exhibits great enhancement in microhardness and wear resistance compared with the H13 substrate.

Influences of preload on the friction and wear properties of high-speed instrument angular contact ball bearings

For starved-oil or solid lubrication of high-speed instrument angular contact ball bearings, friction heating and wear are the main reasons of bearing failures. This paper presents a dynamic wear simulation model to investigate the impacts of different preload methods and the changes of preload caused by wear on bearing wear life. The integral value QV of stress and sliding velocity in the contact ellipses between a ball and the inner and outer races determines friction heating and wear. The changes of QV with the friction coefficient and the wear volume under constantforce preload and fixed-position preload are analyzed. Results show that under the same initial preload, the QV decreases with an increase of the friction coefficient for both preload methods, and the latter is slightly larger. The wear of the ball and the race is equivalent to the ball diameter reduction.The QV of constant-force preload is almost not changed with a decrease of the ball diameter, but for fixed-position preload, the value decreases firstly and then increases substantially due to insufficient preload, and slipping occurs, the ball diameter is reduced by 0.025%, while the preload is reduced by 60.33%. An estimation of the bearing wear life under different preload methods requires a consideration of the changes in the wear rate of bearing parts.

Tribological behavior as lubricant additive and physiochemical characterization of Jatropha oil blends

This investigation reports on the effect of Jatropha oil doped with lube oil on tribological characteristics of Al-7%Si alloy.The factors involved were Jatropha oil percentages,sliding velocities and load which was optimized for weight loss,friction coefficient and specific wear rate characteristics.The conventional lubricant was SAE 40.It is observed that the Jatropha oil percentage factor had significant influence on the weight loss,friction coefficient and wear rate of the pin.The optimum result was A_(2) B_(3) C_(1) for pin weight loss,friction coefficient and wear rate.From the experimental result,it is found that the wear scar diameter increases with the increase of load for lube oil and reduced by addition of percentage of Jatropha oil.Flash temperature parameter was also studied in this experiment and results show that 15%addition of Jatropha oil would result in less possibility to film breakdown.The overall results of this experiment reveal that the addition of 15%Jatropha oil with base lubricant produces better performance and anti-wear characteristics.This blend can be used as lubricant oil which is environment friendly in nature and would help to reduce petroleum based lubricant substantially.

Friction and wear properties of Cu-based self-lubricating composites in air and vacuum conditions

Cu-based self-lubricating materials containing two different solid lubricants （graphite and MoSs） were fabricated by P/M hot pressing techniques. Physical and mechan- ical properties of the samples were examined. The effects of graphite and MoSs contents on friction coefficient and wear rate were investigated by a ring-on-disc wear machine in air and vacuum conditions, respectively. Tribo-films formed on the worn surfaces were characterized by scanning electron microscopy （SEM） and X-ray photo- electron spectroscopy （XPS）. The results indicated that density, hardness and bending strength all increased with the increasing content of MoS2, while the relative density was opposite. Sample B containing 15 vol. pct graphite and 15 vol. pct MoS2 pos- sessed superior tribological properties both in air and vacuum conditions. However, the tribo-films formed on the worn surfaces of the sample B were greatly discrepant in composition at different testing conditions. In air, the volume ratio of MoS2 and graphite in the tribo-films is 0.31：1 whereas the ratio in vacuum is 1.07：1.