Sintering behavior, microstructure and properties of TiC-FeCr hard alloy

TiC based cermets were produced with FeCr, as a binder, by conventional P/M （powder metallurgy） to near 〉97% of the theoretical density. Sintering temperature significantly affects the mechanical properties of the composite. The sintering temperature of 〉1360℃ caused severe chemical reaction between TiC particles and the binder phase. In the TiC-FeCr cermets, the mechanical properties did not vary linearly with the carbide content. Optimum mechanical properties were found in the composite containing 57wt% TiC reinforcement, when sintered at 1360℃ for 1 h. Use of carbon as an additive enhanced the mechanical properties of the composites. Cermets containing carbon as an additive with 49wt% TiC exhibited attractive mechanical properties. The microstructure of the developed composite contained less or no debonding, representing good wettabifity of the binder with TiC particles. Homogeneous distribution of the TiC particles ensured the presence of isotropic mechanical properties and homogeneous distribution of stresses in the composite. Preliminary experiments for evaluation of the oxidation resistance of FeCr bonded TiC cermets indicate that they are more resistant than WC-Co hardmetals.

Effect of Cerium on Microstructures of Hard Alloys

Microstructures and crack extending characteristic of the YG8R,YT5R and YT14R hard alloys adding a trace cerium were studied by AEM and HVEM with a tensile holder.In the hard alloys adding cerium,the compounds of Ce_2O_3 or Ce_2O_2S could be formed,extending of stacking faults and transforma- tion from fcc Co to hcp Co were suppressed,volume fraction of fcc Co in the alloys was increased,and strength of Co and(TiW)C phases and grain boundaries were raised.Plastic deformation in Co phase near edges of the tensile cracks was more strong,and the tensile cracks could pass through some smaller WC grains.

Influence of alloy ingredients on mechanical properties of ternary boride hard alloy clad materials

Using Mo, B-Fe alloy and Fe powders as raw materials, and adding C, Cr and Ni ingredients, respectively, or C, Cr and Ni mixed powders, ternary boride hard alloy clad materials was prepared on Q235 steel substrate by means of in-situ reaction and vacuum liquid phase sintering technology. The influence of alloy ingredients on the mechanical properties of ternary boride hard alloy clad materials was investigated. The results indicate that a mixture of 0.8% C, 5% Cr and 2% Ni ingredients gives a ternary boride hard alloy clad material with optimal mechanical properties, such as high transverse rupture strength, high hardness and good wear resistance.

Refractory Hard Alloys Elaborated by Casting of Ternary (Co, Ni Fe)-30Cr-2.5 to 5 wt% C Compositions

Three series of ternary alloys of the {M-30Cr-xC}-type with M = Co, Ni or Fe and x ranging from 2.5 to 5 wt% were elaborated by casting. Their microstructure characterizations by XRD and SEM show that very high volume fractions in chromium carbides (even more than 50%) may be obtained in a metallic matrix by this way. However graphite may also appear in very low quantities in the carbon-richest alloys. The hardness increases with the carbon content (up to 1000 Hv30kg) but it may be a little lowered when graphite is also present. The results show that very hard alloys may be simply obtained by casting of rather cheap elements.

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.

Effects of high pressure on the microstructure and hardness of a Cu-Zn alloy

The microstructure of a Cu-Zn alloy treated under different high pressures was investigated by means of metallographic, scanning electron microscope （SEM）, energy dispersive spectrometer （EDS）, and X-ray diffraction （XRD）, and the hardness of the Cu-Zn alloy was also measured. The results show that the ct phase with a smaller grain size, different shapes, and random distribution appears in the Cu-Zn alloy during the solid-state phase transformation generation in the temperature range of 25-750℃ and the pressure range of 0-6 GPa. The amount of residual α phase in the microstructure decreases and then increases with increasing pressure. Under a high pressure of 3 GPa, the least volume fraction of residual a phase was obtained, and under a high pressure of 6 GPa, the changes of the microstructure of the Cu-Zn alloy were not obvious. In addition, high pressure can increase the hardness of the Cu-Zn alloy, but it cannot generate any new phase.

Effect of Ca addition on modification of primary Mg_(2)Si,hardness and wear behavior in Mg-Si hypereutectic alloys

The effect of Ca addition on modification of primary Mg_(2)Si,hardness and wear behavior in Mg-5 wt.%Si hypereutectic alloy has been investigated.The results showed clearly that without Ca addition,most of primary Mg_(2)Si appeared as coarse dendritic morphology with average size of about 215μm.With the addition of 0.1 wt.%Ca,the average size of primary Mg_(2)Si decreased to about 98μm,but their morphologies did not significantly changed.As the addition level of Ca increased to 0.3 wt.%,the average size of primary Mg_(2)Si decreased significantly to about 50μm and their morphologies changed to polyhedral shape.However,with further increasing Ca addition to 0.6 wt.%and 1 wt.%,some needle-like and blocky CaMgSi particles formed and the average size of primary Mg_(2)Si increased slightly,which could described as over-modification.The present work showed that the optimal modification effect could be obtained when the Ca content in the investigated alloy reached 0.3 wt.%.The modification mechanism may be referred mainly due to poisoning effect resulting from the segregation of Ca atoms at the growth front of the Mg_(2)Si and the adsorption effect of some Ca atoms in the Mg_(2)Si crystal growth plane.The 0.3 wt.%Ca-added alloy has the highest hardness value and the best wear resistance among all other alloys.An excessive Ca addition resulted in the formation of some needle-like and blocky CaMgSi particles,which was detrimental to hardness and wear behavior of the 0.6 wt.%and 1 wt.%Ca-added alloys.The wear mechanism of investigated alloys is a mild abrasive oxidative wear with little adhesion.

Microstructure characterization and hardness of Al-Cu-Mn eutectic alloy

The composition of Al-Cu-Mn ternary eutectic alloy was chosen to be Al-32.5 wt.%Cu-0.6 wt.%Mn to the Al2 Cu and Al12 Cu Mn2 solid phases within an aluminum matrix(α-Al) from its melt. The Al-32.5 wt.%Cu-0.6 wt.%Mn alloy was directionally solidified at a constant temperature gradient(G=8.1 K·mm^(-1)) with different growth rates, 8.4 to 166.2 μm·s^(-1),by using a Bridgman-type furnace. The eutectic temperature(the melting point) of 547.85 °C for the Al-32.5 wt.%Cu-0.6 wt.%Mn alloy was obtained from the DTA curve of the temperature difference between the test sample and the inert reference sample versus temperature or time. The lamellar spacings(λ) were measured from transverse sections of the samples. The dependencies of lamellar spacings(λAl-Al2 Cu) and microhardness on growth rates were obtained as, λ_(Al-Al2Cu)=3.02 V^(-0.36), HV=153.2(V)^(0.035), HV=170.6(λ)^(-0.09) and HV=144.3+0.82(λ_(AlAl2 Cu))^(-0.50), HV=149.9+53.48 V^(0.25), respectively, for the Al-Cu-Mn eutectic alloy. The bulk growth rates were determined as λ~2_(Al-Al2 Cu)·V = 25.38 μm^3·s^(-1) by using the measured values of λ_(Al-Al2 Cu) and V. A comparison of present results was also made with the previous similar experimental results.

Microstructure, Texture, and Hardness Evolutions of Al-Mg-Si-Cu Alloy during Annealing Treatment

Microstructure, texture and hardness evolutions of Al-Mg-Si-Cu alloy during annealing treatment were studied by microstructure, texture and hardness characterization in the present study. The experimental results show that microstructure, texture and hardness will change to some extent with the increase of annealing temperature. The microstructure transforms from the elongated bands to elongated grains first, and then the grains grow continuously. The texture transforms from the initial deformation texture β fiber to recrystallization texture mainly consisting of CubeND {001}<310> and P {011}<122> orientations first, and then the recrystallization texture may be enhanced continuously as a result of the grain growth. Hardness decreases slowly at first, and then decreases sharply and increases significantly finally. Besides, the particle distributions also have great changes. As the annealing temperature increases, they increase firstly as a result of precipitation, and then gradually disappear as a result of dissolution. Finally, the effect of annealing temperature on microstructure, texture and hardness evolutions is discussed.

Effect of solution treatment on microstructure and hardness of rheo-forming AZ91-Y alloy

The microstructure and hardness of rheo-forming AZ91-Y alloy before and after solution treatment(ST) have been investigated by means of optical microscope(OM), scanning electron microscope(SEM) equipped with energy dispersive spectroscopy(EDS), X-ray diffraction(XRD) and Vickers. The experimental results showed that the β-Mg17Al12 phase of alloy was nearly dissolved after ST for 5 min. With the increasing of ST duration to 28 h, both the primary and secondarily solidified α-Mg grains faded away. At the same time, the alloy exhibited a much smoother surface due to the diffusion of solute atoms(Al). During ST, the thermal stable phase of Al2 Y produced by ultrasonic vibration retained its size and morphology. As the ST duration was increased, the alloy hardness decreased sharply at first, and then gradually reached a minimum level. The alloy's appropriate ST duration at 410 °C was approximately 28 h.

Ageing Effect on Hardness and Microstructure of Al-Zn-Mg Alloys

Experimental results of the investigation on the hardness of two Al-Zn-Mg alloys [Al-10.0 Zn-4.0 Mg and Al-8.5 Zn-3.0 Mg (wt pct)] aged in the temperature range 60～310℃ for different intervals of time from 1/4 h to 168 h are presented. Both the alloys were found to show identical behaviour of hardness with ageing time. Alloy with higher Zn and Mg content had higher hardness than the alloy with lower solute content. There were three ranges of temperature in which different types of precipitates formed and affected the hardness. Some of the grain boundaries were found to migrate and precipitate free zone has been observed.

Effect of experimental parameters on the micro hardness of plasma sprayed alumina coatings on AZ31B magnesium alloy

Surface treatment of engineering materials has recently become important for serviceable engineering components.Many techniques such as thermal and thermo chemical surface treatments have been used to develop surface characteristics of materials.Hardness is the most important property,which influences considerably service life characteristics of coatings.In this investigation,alumina coatings were deposited by atmospheric plasma spray technique under different levels of power,stand-off distances and powder feed rates.Empirical relationship was developed to predict the micro hardness of alumina coatings by incorporating the plasma spray process parameters.The input power and the stand-off distance appeared to be the most significant two parameters affecting the hardness of the coating among the three investigated process parameters.Further,correlating the spray parameters with coating properties enables the identification of characteristics regime to achieve desired quality of coatings.

Effect of Heat Treatment on Hardness and Impact Toughness of CuCr Containing RE Alloy

The effect of heat treatment on hardness and impact toughness of CuCr containing rare earth alloy was studied by means of metallographic, XRD, SEM/EDX, TEM and mechanical property test. The results show that the heat treatment can change the hardness of CuCr alloy, and has smaller influence to its impact toughness. The optimum properties of CuCr containing RE alloy could be obtained by aging treatment at 500 ℃ for 2 h. And the causes of the above changes and the function of RE were analyzed.

Homogeneity of microstructure and Vickers hardness in cold closed-die forged spur-bevel gear of 20Cr Mn Ti alloy

Cold closed-die forging is a suitable process to produce spur-bevel gears due to its advantages, such as saving materials and time, reducing costs, increasing die life and improving the quality of the product. The homogeneity of microstructure of cold closed-die forged gears can highly affect their service performance. The homogeneity of microstructure and Vickers hardness in cold closed-die forged gear of 20 Cr Mn Ti alloy is comprehensively studied by using optical microscopy and Vickers hardness tester. The results show that the distribution homogeneity of the aspect ratio of grain and Vickers hardness is the same. In the circumferential direction of the gear tooth, the distribution of the aspect ratio of grain and Vickers hardness is inhomogeneous and they gradually decrease from the surface to the center of the tooth. In the radial direction, the distribution of the aspect ratio of grain and Vickers hardness is inhomogeneous on the surface of the gear tooth; while it is relatively homogeneous in the center of the gear tooth. In the axial direction of the gear tooth, the distribution of the aspect ratio of grain and Vickers hardness is relatively homogeneous from the small-end to the large-end of the gear tooth.

Formation and thermal stability of connected hard skeleton structure in ATX525 cast alloys

The formation and the thermal stability of a connected hard skeleton structure(CHSS) in the matrix of Mg-5Al-2Sn-5Ca(ATX525) alloy were investigated by using X-ray diffractometer, scanning electron microscopy, differential scanning calorimeter, creep tester and isothermal treatment method. The results indicated that the CHSS composed of Mg2(Al,Ca) and Al2 Ca intermetallics was formed into a typical eutectic structure and no obvious change occurred when the samples were isothermally treated at 250 °C for 96 h and 350 °C for 72 h, respectively. It became a chained structure when isothermally treated at 450 °C for 48 h. The dissolution and reconstruction processes, however, were observed for the CHSS when the processing temperature was up to 550 °C. The creep life at the stress-temperature condition of 50MPa/200°C for the alloy treated at 450 °C for 48 h was as high as 510 h, and the strain at creep time of 100 h was as low as 0.03%, which indicated that the present alloy has not only a good thermal stability, but also a better heat resistance.

Influence of alloying elements on microstructure and microhardness of Mg-Sn-Zn-based alloys

阶段进化在(88%-91%) Mg-8%Sn-1%Zn-X (X=Al， Mn 或 Ce ) 系统经由 CALPHAD 方法被分析，模拟在化学作文的精确选择被使用。象 Mg-8%Sn-1%Zn-based 合金的微观结构和 microhardness 上的艾尔， Mn 和 Ce 那样的不同 alloying 元素的增加的影响被调查。艾尔和 Mn 的联合增加显示出从艾尔或 Mn 的分开的增加不同的特征。到基础合金的 1%Al 和 1%Mn 的增加在 -Mg 矩阵谷物导致巨大的 Al-Mn 阶段的形成。Ce 元素的增加能精制第二最容易溶解猛抛并且与 Sn 形成金属间化合的混合物。好像杆的 Sn-Ce 阶段主要在谷物边界上介绍并且在禁止谷物生长起一个作用。Vickers microhardness 上的 alloying 元素的效果和基础合金的缩进尺寸效果被检验。

Effect of homogenization process on the hardness of Zn-Al-Cu alloys

The effect of a homogenizing treatment on the hardness of as-cast Zn–Al–Cu alloys was investigated. Eight alloy compositions were prepared and homogenized at 350 °C for 180 h, and their Rockwell 'B' hardness was subsequently measured. All the specimens were analyzed by X-ray diffraction and metallographically prepared for observation by optical microscopy and scanning electron microscopy. The results of the present work indicated that the hardness of both alloys(as-cast and homogenized) increased with increasing Al and Cu contents; this increased hardness is likely related to the presence of the θ and τ′ phases. A regression equation was obtained to determine the hardness of the homogenized alloys as a function of their chemical composition and processing parameters, such as homogenization time and temperature, used in their preparation.

Hard Magnetic Properties of Sm-Fe-C Based Alloys Prepared by Mechanical Alloying

The structure and magnetic properties of SmyFe100-1.5yC0.5y(y=8～20) alloys prepared by mechanical alloying (MA) from Sm, Fe and graphite have been investigated systematically. In order to improve hard magnetic properties of the alloys prepared by mechanical alloying, a new method consisting of re-milling and re-annealing was developed. After being re-milled and re-annealed, the Curie temperature TC of the Sm-Fe-C alloys changes. The TC of 2:17 phase increases, whereas the TC of 2:14:1 phase decreases. After being re-annealed at low temperatures, the grain sizes of hard phases are smaller than those in the alloys annealed at high temperatures. The effects of Co or Ti substitution for Fe are studied.

Correlation between Hardness, Structure and Electrochemical Performance of an AlZnMnMg Alloy

In this work the structural changes induced by aged treatment have shown a connection with differences of hardness and electrochemical performance. Al-base alloys have been investigated by means of Vickers hardness, X-ray diffraction, scanning electron and short-term electrochemical test. X-ray diffraction result reveals the formation of (MgZn)49Al32 phase for two conditions, the first one is when the magnesium content is upper to 5.49% in as-cast condition and the second one after the thermal treatment carried out at 450?C for 5 h. In addition, the hardness and electrochemical performance has been influenced by the presence and quantity of the (MgZn)49Al32 phase. The addition of magnesium alloying modifies the microstructure, increases the content of (MgZn)49Al32 phase and provides a localized corrosion which conduced to the breakdown of the oxide film (?-Al2O3) formed on the Al alloy surface.

Research on lamellar structure and micro-hardness of directionally solidified Sn-58Bi eutectic alloy

In this work,the Sn-58Bi(weight percent) eutectic alloy was directionally solidified at a constant temperature gradient(G = 12 K.mm-1) with different growth rates using a Bridgman type directional solidification furnace.A lamellar microstructure was observed in the Sn-58Bi samples.The lamellar spacing and micro-hardness of longitudinal and transversal sections were measured.The values of lamellar spacing of both longitudinal and transversal sections decrease with an increase in growth rate.The microhardness increases with an increase in the growth rate and decreases with an increase in the lamellar spacing.The dependence of lamellar spacing on growth rate,and micro-hardness on both growth rate and lamellar spacing were obtained by linear regression analysis.The relationships between the lamellar spacing and growth rate,microhardness and growth rate,and micro-hardness and lamellar spacing for transversal and longitudinal sections of Sn-58Bi eutectic alloy were given.The fitted exponent values obtained in this work were compared with the previous similar experimental results and a good agreement was obtained.