Development of wear resistant composite surface on mild steel by laser surface alloying with silicon and reactive melting

The present study concerns laser surface alloying with silicon of mild steel substrate using a high-power continuous wave CO₂ laser with an objective to improve wear resistance. The effect of surface remelting using nitrogen as shrouding environment (with and without graphite coating) on microhardness and wear resistance has also been evaluated. Laser surface alloying leads to formation of a defect free microstructure consisting of iron silicides in laser surface alloyed mild steel with silicon and a combination of silicides and nitrides when remelted in nitrogen. Carbon deposition prior to remelting leads to presence of a few martensite in the microstructure. A significant improvement in microhardness is achieved by laser surface alloying and remelting to a maximum of 800 VHN when silicon alloyed surface is melted using nitrogen shroud with carbon coating. A detailed wear study (against diamond) showed that a significant improvement in wear resistance is obtained with a maximum improvement when remelted in nitrogen atmosphere followed by carbon coating.     

Studies on fly ash/coir/sugarcane reinforced epoxy polymer matrix composite

In the past years studies were conducted on natural fibre reinforced polymer composites to observe their mechanical properties in order to decide their industrial applications. These composites have already been used in many applications from aerospace to sporting equipment. These green composites can be used as a replacement for synthetic composites. This is because the natural fibres are eco-friendly, biodegradable, renewable, etc. In this work, an attempt is made to reinforce fly ash, coir fibre and sugarcane fibre with epoxy polymer matrix. Central composite design under response surface methodology (RSM), one of the approaches of design of experiments (DOE) is used to determine optimum sample preparation conditions of fly ash, coir fibre and sugarcane fibre. Both tensile and flexural (three-point bending) tests are conducted on these fabricated composites to determine their materialistic characteristics. Analysis of variance (ANOVA) is carried out using Minitab software to find the influence of fly ash, coir fibre, sugarcane fibre on composites. Regression equations obtained from analysis of variance is used to calculate values. Experimental and calculated values are compared and their error % are calculated and tabulated. Response surface optimization study is carried to find the optimized parameters of composites. It is observed that, increase in wt.% of coir fibre and decrease in wt.% of fly ash and sugarcane fibre, increases yield stress and these parameters have mixed impact on ultimate tensile stress. The addition of fly ash, coir fibre and sugarcane fibre in low percentages increases Young's modulus. Increase in wt.% of fly ash and coir fibre and decrease in wt.% of sugarcane, increases flexural modulus and flexural stress.     

Microstructures, densification and mechanical properties of TiC–Al2O3–Al composite by field-activated combustion synthesis

Dense TiC–Al₂O₃–Al composite was prepared with Al, C and TiO₂ powders by means of electric field-activated combustion synthesis and infiltration of the molten metal (here Al) into the synthesized TiC–Al₂O₃ ceramic. An external electric field can effectively improve the adiabatic combustion temperature of the reactive system and overcome the thermodynamic limitation of reaction with x < 10 mol. Thereby, it can induce a self-sustaining combustion synthesis process. During the formation of Al₂O₃–TiC–Al composite, Al is molten first, and reacted with TiO₂ to form Al₂O₃, followed by the formation of TiC through the reaction between the displaced Ti and C. Highly dense TiC–Al₂O₃–Al with relative density of up to 92.5% was directly fabricated with the application of a 14 mol excess Al content and a 25 V cm⁻¹ field strength, in which TiC and Al₂O₃ particles possess fine-structured sizes of 0.2–1.0 μm, with uniform distribution in metal Al. The hardness, bending strength and fracture toughness of the synthesized TiC–Al₂O₃–Al composite are 56.5 GPa, 531 MPa and 10.96 MPa m^1/2, respectively.     

Experimental investigation on mechanical properties and wear characterization of Al-Si12CulMg1 aluminium alloy reinforced with titanium diboride and boron carbide particulate hybrid composites using stir casting process

LM13 aluminium alloy (Al−Si12CulMg1) with titanium diboride (TiB₂) and boron carbide (B₄C) particulate hybrid composites have been prepared using stir casting process. Wt% of titanium diboride is varied from 0–10 and constant 5 wt% boron carbide particles have been used to reinforce LM13 aluminium alloy. Microstructure of the composites has been investigated and mechanical properties viz., hardness, the tensile strength of composites have been analyzed. Wear behavior of samples has been tested using a pin on disc apparatus under varying load (20 N–50 N) for a sliding distance of 2000 m. Fracture and wear on the surface of samples have been investigated. Microstructures of composites show uniform dispersion of particles in LM13 aluminium alloy. Hardness and tensile strength of composites increased with increasing wt % of reinforcements. Dry sliding wear test results reveal that weight loss of composites increased with increasing load and sliding distance. Fracture on the surface of composites reveals that the initiation of crack is at the interface of the matrix and reinforcement whereas dimples are observed for LM13 aluminium alloy. Worn surface of composites shows fine grooves and delamination is observed for the matrix.     

基于纤维模型的型钢混凝土组合剪力墙滞回性能分析

为更深入研究型钢混凝土剪力墙的抗震性能,在已有该类剪力墙滞回性能试验结果基础上,采用OpenSees软件中非线性纤维梁-柱单元进行低周往复加载的数值模拟,通过直接在截面层次定义非线性剪切恢复力方法模拟纤维截面的抗剪。计算结果与试验结果总体吻合较好,表明该纤维模型法能较好模拟型钢混凝土剪力墙的抗剪承载力、捏缩效应及刚度退化。该方法可为此类结构体系的弹塑性分析提供参考。     

Effect of post-weld heat treatment on the interface microstructure of explosively welded titanium–stainless steel composite

In this study, the interface microstructure evolutions of the explosively welded cp-Titanium/AISI 304 stainless steel composites due to heat treatment are presented. The composites were subjected to heat treatment process at temperature ranges of 650–950 °C in argon atmosphere for 1 h. The investigations were carried out by using optical microscopy (OM), scanning electron microscopy (SEM). The results reveal the presence of reaction layers in the diffusion zone. The compositions of the reaction products were determined by energy dispersive spectroscopy (EDS). Furthermore, the composition–penetration plots for Ti, Fe, Cr and Ni across the interface were obtained from EDS microanalysis. Concentration of discontinuities in the profiles indicating the formation of intermetallics in the diffusion zone that were also detected by X-ray diffraction (XRD) method, on the Ti-side of fractured surfaces. The results show that post-heating of the composite layers in these temperatures causes to form different intermetallic phases at the joint interface. Moreover, post-heating increases the width of interfacial layers of the composite.     

The inhibition of 4-(2′-amino-5′-methylphenylazo) antipyrine on corrosion of mild steel in HCl solution

The effect of 4-(2′-amino-5′-methylphenylazo) antipyrine (AMPA) on the corrosion of mild steel in a 2 M HCl solution was studied using weight loss and potentiodynamic polarization techniques. All of the data reveal that AMPA acts as an inhibitor in the acid environment; furthermore, polarization data show that the compound behaves as a mixed-type inhibitor. It was found that the inhibition efficiency increases with an increase in AMPA concentration but decreases with an increase in temperature. Flory–Huggins adsorption isotherm and El Awady thermodynamic–kinetic model fit the experimental data of the studied compound. Thermodynamic parameters for corrosion and adsorption processes were obtained from experimental data of the temperature studies.     

The effects of disbonds on the pure mode II stress intensity factor of aluminium plate reinforced with bonded composite materials

Adhesively bonded composite patch repair has been widely used to restore or extend the service life of cracked structural components due to its effectiveness to mechanical repair technique. In this work, the finite element method is applied to analyse the performance of the bonded composite patch for repairing cracks emanating from semicircular notch root in pure mode II. The stress intensity factor was computed at the crack tip repaired using a boron/epoxy patch for different orientation of fibers, taking into account the disbond. In this case, the increase of a patch thickness reduces the negative effects of disbond. When this effect is significant between the patch and the plate, it reduces the repair effectiveness. The maximum reduction obtained by using a boron/epoxy of fibers in the x-direction is of the order of 20% more important compared to a patch having its fibers in the y-direction. The stress intensity factor exhibits an asymptotic behaviour as the disbond size increases.     

The effect of Li on the tensile properties of cast Al–Mg2Si metal matrix composite

The effects of both Li modification and cooling rate on the microstructure and tensile properties of an in situ prepared Al–15%Mg₂Si composite were investigated. It was found that the addition of 0.3%Li reduces the average size of Mg₂Si primary particles from 30 to 6 μm. The effect of cooling rate was investigated by the use of a mold with different section test bars. The results showed an increase in both UTS and elongation values with reduction in section thicknesses corresponding to increasing cooling rates. Adding Li also raised the tensile strength and elongation values and reduced the number of decohered particles observed in fracture surfaces thereby increasing the alloy's ductility. Data scatter and unexpected low tensile values of 3 mm sections were attributed to casting defects observed in fracture surfaces. Large clusters of Mg₂Si particles and eutectic cell boundaries were found to be potential crack propagation paths in this alloy.     

Effect of small γ-precipitates on the two-way shape memory effect in Cu–Zn–Al alloys

The γ-precipitates in Cu–Zn–Al alloys, trained by the stabilization of the stress induced martensite (SSIM) method, have been studied. After the SSIM treatment, it was found that small γ-precipitates in the β-austenite are ellipsoidal, with a large strain field oriented in the same direction; while in the martensite the γ-precipitates changed their shape from ellipsoid to spheroid, and relaxed their strain fields. In order to check whether the strain field of the γ-precipitates is capable of producing a thermoelastic martensitic transformation, an in-situ observation, by heating a sample holder in TEM, was performed. It was found that during heating over a temperature A_s, the γ-precipitates with a spherical shape in the martensite recovered their strain field and elliptical shape. During cooling, the strain field of the γ-precipitates disappeared again. It was proposed that the strain field of the γ-precipitates, trained by the SSIM method, plays an important part in the thermoelastic martensitic transformation, and presents two-way shape memory effects.     

Effects of screen-grid bias voltage on the microstructure and properties of the ultrahigh molecular weight polyethylene (UHMWPE) modified by oxygen plasma

The specimens of ultrahigh molecular weight polyethylene (UHMWPE) were treated by oxygen plasma using a pulse-biased screen-grid technique under different negative bias conditions. The screen-grid was used to provide an electric field to accelerate the oxygen ions towards the UHMWPE substrate during the plasma treatment process. The effects of the screen-grid voltage on the surface microstructure, wettability, mechanical properties and wear resistance of UHMWPE were investigated. It was found that the degree of crosslinking, oxidation, wettability and surface roughness of UHMWPE can be increased with the increasing of the screen-grid voltage. Owing to the increase of the degree of crosslinking, the hardened layer formed on the surface of the UHMWPE samples was also strengthened greatly with the increase of the grid voltage. However, the wear results indicated that the UHMWPE sample modified at higher bias voltage exhibits poor wear performance, which could be mainly related to the embrittlement resulted from the aggravation of oxidation.     

Studies on the formation of Langmuir monolayer and Langmuir–Blodgett films of octadecyl amine-bromocresol purple dye complex

Properties of the monolayer of octadecyl amine (ODA) molecules on aqueous solution of bromocresol purple (Bcp) dye have been studied over a wide range of pH by measuring the surface pressure-area isotherms. A strong interaction of ODA molecule was observed with the dye molecule in the pH range of 4–9. Under the present study, the dye molecules were adsorbed on the ODA monolayer at the water surface and subsequently a Langmuir–Blodgett (LB) film of ODA–dye complex was transferred from the air–water interface onto a solid substrate. Alternatively, dye molecules were incorporated into LB film by immersing the predeposited LB film of pure ODA into the dye solution, i.e. by adsorption of dye molecule at the solid–liquid interface. The adsorption behavior of ODA–Bcp dye complexes obtained through these two different routes was characterised with the help of UV–Visible spectroscopy. The nature of the ODA–dye complex deposited from air–water interface using the LB technique was found to be quite different from that of the complex formed by the adsorption of the dye into the pure ODA LB film. The adsorption spectra of the ODA–dye complex obtained from the air–water interface did not change with pH, while those of the ODA–dye complex formed from the solid–liquid interface showed pH dependence.     

Influence of the microstructure on the corrosion resistance of plasma‐nitrided austenitic stainless steel 304L and 316L

Austenitic stainless steels are widely used in medical and food industries because of their excellent corrosion resistance. However, they suffer from weak wear resistance due to their low hardness. To improve this, plasma nitriding processes have been successfully applied to austenitic stainless steels, thereby forming a thin and very hard diffusion layer, the so‐called S‐phase. In the present study, the austenitic stainless steels AISI 304L and AISI 316L with different microstructures and surface modifications were used to examine the influence of the steel microstructure on the plasma nitriding behavior and corrosion properties. In a first step, solution annealed steel plates were cold‐rolled with 38% deformation degree. Then, the samples were prepared with three kinds of mechanical surface treatments. The specimens were plasma nitrided for 360 min in a H₂–N₂ atmosphere at 420 °C. X‐ray diffraction measurements confirmed the presence of the S‐phase at the sample surface, austenite and body centered cubic (bcc)‐iron. The specimens were comprehensively characterized by means of optical microscopy, scanning electron microscopy, glow discharge optical emission spectroscopy, X‐ray diffraction, surface roughness and nano‐indentation measurements to provide the formulation of dependencies between microstructure and nitriding behavior. The corrosion behavior was examined by potentio‐dynamic polarization measurements in 0.05 M and 0.5 M sulfuric acid and by salt spray testing.     

Effect of Creep and Aging on the Precipitation Kinetics of an Al–Cu Alloy after One Pass of ECAP

Recent work shows that severe plastic deformation processes such as ECAP or HPT considerably accelerate the precipitation kinetics of Al‐Cu alloys. In this study, the authors analyze how a combination of mechanical load, aging time (and increased plastic strain), and aging temperature affects the precipitation kinetics of an AA2017 alloy after ECAP. After solution annealing, the material is processed by one pass of ECAP (120°‐channel angle) at 140 °C. Compressive creep tests are performed on the initial condition and the ECAP‐deformed material. The resulting microstructures are studied in detail using electron microscopy. To investigate the influence of mechanical loading, interrupted compressive creep tests are performed and compared with aged samples (produced without any mechanical loading at the same temperature and after the same amount of time). By keeping time and load constant in another set of interrupted compressive creep tests, the influence of temperature is investigated. Our study shows that increasing mechanical loading further accelerates the precipitation kinetics. Temperature accelerates the precipitation kinetics as well, but results in coarser precipitates. The authors also find that different creep strains can lead to the formation of two different regions in the microstructure: regions with only a few coarsened θ‐phase precipitates, and regions with numerous, finely dispersed precipitates.     

Effect of loading rate on the monotonic tensile behavior and tensile strength of an oxide–oxide ceramic composite at 1200 °C

The influence of loading rate on monotonic tensile behavior and tensile properties of an oxide–oxide ceramic composite was evaluated in laboratory air at 1200 °C. The composite consists of a porous alumina matrix reinforced with woven mullite/alumina (Nextel™720) fibers, has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. Tensile tests conducted at loading rates of 0.0025 and 25 MPa/s revealed a strong effect of rate on the stress–strain behavior as well as on the ultimate tensile strength (UTS), elastic modulus and failure strain. At 0.0025 MPa/s, increase in stress results in non-monotonic change in strain, with the rate of change of strain reversing its sign at stresses 25 MPa/s. Several samples were subjected to additional heat treatments prior to testing in order to determine whether this unusual stress–strain behavior was an artifact of incomplete processing of fibers in the as-received material. The unusual material response in the 0–30 MPa stress range was further investigated in creep tests conducted with the applied stresses ≤26 MPa. Negative creep (i.e. decrease in strain under constant stress) was observed. Porosity measurements indicate that a decrease in matrix porosity and matrix densification may be taking place in the N720/A composite exposed to 1200 °C at stresses <30 MPa for prolonged periods of time.     

基于试验设计的膨胀型钢结构防火涂料配方的多变量分析(英文)

膨胀型防火涂料的配方优化,需要阻燃剂之间有效的协同作用来获得防火效果。以ISO耐火测试标准为依据,对以聚磷酸铵、季戊四醇和三聚氰胺阻燃剂为主要成分的防火涂料,利用D-优化设计原理,借助Design Expert软件进行试验设计,在有限的试验次数基础上,运用MODDE软件对试验结果进行了多变量回归分析,获得了满意的试验结果。     

Influence of the Al(Co,Ni) layer on the corrosion resistance of a cobalt based alloy (Mar‐M‐509®)

In the present work, the results of studies on the structure and corrosion resistance of Al(Co, Ni) layer are shown. The diffusion Al(Co, Ni) layer was created on the cobalt alloy Mar‐M‐509 substrate by chemical vapor deposition (CVD) method with aluminum trichloride (AlCl₃) under the hydrogen atmosphere. The scanning electron microscope (SEM) observations and microtomography measurements of layers were performed. Also an analysis of the chemical (energy‐dispersive X‐ray spectroscopy (EDS)) and phase (X‐ray diffraction (XRD)) composition was carried out. By the X‐ray diffraction method (sin² φ) also the residual stresses were calculated in the matrix of the material. The corrosion resistance was tested with impedance and potentiodynamic methods in 0.1 M Na₂SO₄, 0.1 M H₂SO₄ solutions and acidulous 0.1 M NaCl solution (pH = 4.2) at room temperature. The results indicate that the analyzed layer with a thickness of about 14 μm have a similar corrosion resistance compared to the base material – Mar‐M‐509^® cobalt alloy. Only in the strongly acidic environments, the corrosion resistance of the layer is remarkably decreased.     

The compression/absorption cycle – influence of some major parameters on COP and a comparison with the compression cycleLe cycle à compression–absorption: influence de certains paramètres importants sur le COP et comparaison avec le cycle à compression

This article concerns two main studies: a parameter study and a comparison. In the parameter study, the CAHP is focused upon. Its COP sensitivity to changes in the absorber and desorber falling-film tube length, heat exchanger area distribution, and concentration change of the solution in the absorber is studied. The relative distribution between the desorber and absorber is found to have little impact on COP. The area distributed to the solution heat exchanger and the concentration change in the absorber is found to have a large impact on COP when examined separately, but when they are studied together, and with optimized concentration change for each area distribution, the total impact is low. It is shown that the falling-film tubes should be designed to be as long as possible in order to increase the COP.The comparison involves a new procedure for comparing the performance (COP) of a compression/absorption heat pump (CAHP) with that of a compression heat pump (CHP). In the procedure local heat transfer coefficients and pressure drop are taken into account. Further, the comparison is performed for various heating applications and with specified investment level. The heating applications are typically industrial or district heating cases and are chosen to study impact of three different kinds: size of the sink and source temperature change (glide), temperature lift for a given sink and source glide and temperature level for a given sink and source glide. Ammonia/water is used as working fluid in the CAHP and isobutane in the CHP. A relevant industrial design is assumed for the CHP (including an indirect economizer coupling, suction gas heat exchanger, sub-cooler and surface enhancements in evaporator and condenser), which is not the case in previous comparisons of this type. The absorber and desorber in the CAHP are modeled as vertical falling-film tube-and-shell heat exchangers. The main results for the comparison study are: (1) the COP of the CAHP is as good as that of the CHP when the sink and source glides are 10 K; (2) when the glide of the sink and source is increased to 20 K, the CAHP has a 12% better performance than the CHP; and (3) an increased temperature lift and an increased temperature level give the CAHP a relatively worse COP. Some COP-increasing design parameters to be studied further are proposed for the CAHP.     

The influence of the molar ratio of Al2O3 to Y2O3 on sintering behavior and the mechanical properties of a SiC–Al2O3–Y2O3 ceramic composite

The influence of the molar ratio of Al₂O₃ to Y₂O₃ (i.e. M_Al2O3/M_Y2O3) on sintering densification, microstructure and the mechanical properties of a SiC–Al₂O₃–Y₂O₃ ceramic composite were studied. It was shown that the optimal value of M_Al2O3/M_Y2O3 was 3/2, not 5/3, which is customarily considered the optimal molar ratio for the formation of YAG (Y₃Al₅O₁₂) phase. When M_Al2O3/M_Y2O3 is 5/3, materials existed in two phases of YAG and very little YAM phases. The sintering mechanism of the solid phase occurred at 1850 °C. When M_Al2O3/M_Y2O3 was 3/2, materials existed in the two phases YAG (Y₃Al₅O₁₂) and YAM (Y₄Al₂O₉). The formation of the low melting point eutectic liquid phase (YAG + YAM) increased sintering densification. Flexure strength, hardness and relative density were all higher.