Room Temperature Hardness Research Articles

Microstructures and Mechanical Properties of Two-Phase FeNiMnAl Alloys

This paper presents an overview of the microstructures found in a range of two-phase FeNiMnAl alloys ranging from near-equiatomic very high-strength nanostructured alloys, such Fe30Ni20Mn25Al25, to more ductile f.c.c./B2 alloys, such as Fe30Ni20Mn35Al15. The effect of annealing at 823 K on the room temperature hardness is presented together with the temperature dependence of the yield strength.

Fabrication and characterization of reference 9Cr and 12Cr-ODS low activation ferritic/martensitic steels

For the purpose of arranging reference alloys available for various characterization efforts by Japanese fusion research groups, fabrication of reference 9Cr and 12Cr-ODS steels have been carried out with similar manufacturing processes followed by various characterizations. The fabrication proceeded with powder mixing, MA, encapsulation into mild steel cases, hot extrusion and hot forging, followed by final heat treatments. Each alloy was extruded into three bars. The characterization included chemical composition analysis, SEM and TEM microstructural observations, hardness tests, tensile tests at RT and 973K, and relatively short-term thermal creep tests at 973K. Room temperature hardness for 9Cr-ODS was larger than 12Cr-ODS, the former showing large increase when annealing temperature exceeded 1200K and the latter showing no significant change with annealing temperature. Tensile strength of 9Cr-ODS was significantly larger than that of 12Cr-ODS at RT but comparable at 973K. 9Cr-ODS showed longer and shorter creep rupture time than 12Cr-ODS at high and low stress levels, respectively. The mechanism of the difference in creep properties of the two alloys was discussed.

Densification and characterization of spark plasma sintered ZrC–ZrO2 composites

ZrC based composites alloyed by nanosized tetragonal 3mol% yttria stabilized zirconia were produced with spark plasma sintering to >98% of the theoretical density by sintering at 1900°C under pressure of 50MPa for 10min. The volume fraction of stabilized zirconia varied from 25 to 40vol% in the precursor powder blend. Room temperature hardness and modulus of elasticity of the compacts were in the range reported earlier for similar materials densified by pressureless sintering, while indentation fracture toughness was around 7MPam1/2. Structural analysis indicated formation of oxycarbides of various stoichiometries.

Yield Strength of Hot Forging Die Steels at Working Temperatures

One mode that limits the usefulness of hot forging die steels is localized plastic deformation in regions of high pressure. To understand this behavior the yield strength of the steel needs to be measured at working temperatures in order to determine the likelihood of localized plasticity. One of the issues in using die steels for hot forging applications is that they are initially tempered to a hardness value when put into service. As the die is used to produce forged components, the contact with the hot forging causes the die to continue to temper and hence soften with continued used. To explore these issues three different die steels were obtained and tested experimentally. Experimental compressive yield strengths were determined for the three die steels (FX, 2714 and WF). The die steels were tempered to various hardness values prior to compression testing. The five room-temperature hardness values after tempering ranged from 20 to 38 HRC. The five temperatures for compression testing ranged from 593 to 704 °C (1100 to 1300 oF). From these tests a good characterization of the high temperature plastic behavior of each steel was obtained. It was found that the WF steel which had the highest alloy content was the strongest of the three steels under all test conditions. The FX and 2714, which had similar alloy contents (with FX having slightly less carbon, nickel and vanadium), had yield strengths that were close to each other at the intermediate temperatures, but at the high and low end of the testing range for temperature the FX was stronger than the 2714. Hence, to obtain the greatest resistance to localized plastic deformation during operations the choice of die steel should be WF, followed by FX and then 2714.

Structural characteristics and elevated temperature mechanical properties of AJ62 Mg alloy

Structure and mechanical properties of the novel casting AJ62 (Mg–6Al–2Sr) alloy developed for elevated temperature applications were studied. The AJ62 alloy was compared to commercial casting AZ91 (Mg–9Al–1Zn) and WE43 (Mg–4Y–3RE) alloys. The structure was examined by scanning electron microscopy, x-ray diffraction and energy dispersive spectrometry. Mechanical properties were characterized by Viskers hardness measurements in the as-cast state and after a long-term heat treatment at 250°C/150hours. Compressive mechanical tests were also carried out both at room and elevated temperatures. Compressive creep tests were conducted at a temperature of 250°C and compressive stresses of 60, 100 and 140MPa. The structure of the AJ62 alloy consisted of primary α-Mg dendrites and interdendritic nework of the Al4Sr and massive Al3Mg13Sr phases. By increasing the cooling rate during solidification from 10 and 120K/s the average dendrite arm thickness decreased from 18 to 5μm and the total volume fraction of the interdendritic phases from 20% to 30%. Both factors slightly increased hardness and compressive strength. The room temperature compressive strength and hardness of the alloy solidified at 30K/s were 298MPa and 50 HV 5, i.e. similar to those of the as-cast WE43 alloy and lower than those of the AZ91 alloy. At 250°C the compressive strength of the AJ62 alloy decreased by 50MPa, whereas those of the AZ91 and WE43 alloys by 100 and 20MPa, respectively. The creep rate of the AJ62 alloy was higher than that of the WE43 alloy, but significantly lower in comparison with the AZ91 alloy. Different thermal stabilities of the alloys were discussed and related to structural changes during elevated temperature expositions.

Effect of Ta substitution method on the mechanical properties of Ni3(Si,Ti) intermetallic alloy

In this study, Ta was added to an L12-type Ni3(Si,Ti) alloy at different levels and into different substitution sites, substituting for either Ni, Ti or Si. The solubility limits of Ta in the L12 phase were 1.9at%, 5.7at% and 1.0at% when Ta substituted for Ni, Ti and Si, respectively. The lattice parameters in the L12 phase region increased in the order of the Ta(Ni)>Ta(Si)>Ta(Ti) quaternary alloys, in which Ta substituted for Ni, Si and Ti, respectively. The room-temperature hardness in the L12 phase region increased linearly with increasing Ta content, and the increment rate increased in the order of the Ta(Ni)>Ta(Si)>Ta(Ti) quaternary alloys. Similarly, the room-temperature 0.2% proof stress as well as the tensile strength in the L12 phase region increased linearly with increasing Ta content, and the increment rate increased in the order of the Ta(Ni)>Ta(Si)>Ta(Ti) quaternary alloys. High tensile elongation was observed at room temperature when the microstructures remain in the L12 single phase. At high temperatures, a positive temperature dependence of the hardness as well as the flow strength was observed in the quaternary alloys. It was also shown that the wear resistance of the quaternary Ta(Ti) alloys was improved and attributed to plastically induced hardening of the worn surfaces combined with the positive temperature dependence of the flow strength. The strengthening and hardening resulting from Ta addition was suggested to be due to the hardening of the solid solution arising from the misfits in the atomic radius between Ta and the constituent atoms Ni, Ti or Si.

Microstructure and mechanical properties of two-phase Fe30Ni20Mn20Al30. Part I: Microstructure

The microstructure of Fe30Ni20Mn20Al30 in both the as-cast condition and after annealing at 823 K for various times up to 72 h was characterized using transmission electron microscopy, scanning transmission electron microscopy, synchrotron-based X-ray diffraction, and atom probe tomography. The microstructure exhibited a basketweave morphology of (Mn, Fe)-rich B2-ordered (ordered b.c.c.) and (Ni, Al)-rich L21-ordered (Heusler type) phases with a lattice misfit of only 0.85 % and interfaces aligned along 〈100〉. The phase width increased from 5 nm for the as-cast alloy to 25 nm for 72 h annealed material, with no change in the elemental partitioning between the phases, with a time exponent for the coarsening kinetics of 0.19. Surprisingly, it was found that the room temperature hardness was largely independent of the phase width.

Room temperature hardness of gadolinia-doped ceria as a function of porosity

Porous gadolina-doped ceria (Ce0.9Gd0.1O1.95, GDC10) is commonly used as a functional electrode support in solid oxide fuel cells, gas sensors, and gas separators. In addition, dense GDC10 is commonly used as a solid oxide fuel cell electrolyte and a gas separation membrane. Although, porosity affects a wide range of electrical, thermal, and mechanical properties of solids, this study focuses on (i) the Vickers indentation hardness, H, as a function of volume fraction porosity, P, ranging from 0.08 to 0.60 and (ii) the load dependence of H for Vickers indentation loads of 0.98–9.8 N. For the 13 GDC10 included in this study, the decrease in H with increasing P is approximated by the empirical relationship H = H 0 exp(−b H P), where H 0 = 5.844 GPa and b H = 6.68. In addition, the H values were roughly independent of the applied load.

Thermophysical, mechanical and dielectric studies on piperidinium p-hydroxybenzoate

Single crystals of recently identified nonlinear optical material, piperidinium p-hydroxybenzoate (PDPHB), were grown by solution cooling method. It crystallizes in a monoclinic system with a noncentrosymmetric space group Cc. Thermal stability and decomposition behavior of PDPHB are illustrated through thermogravimetric, differential thermal and differential calorimetric analysis. The thermal diffusivity, thermal conductivity, and specific heat capacity of the grown crystals, which are the three most important thermo-physical parameters in heat transfer calculations, are calculated by an improved photopyroelectric technique. The room temperature hardness test has been performed on crystallographic planes (200), (020), and (002) using Vickers microhardness tester and the results are analyzed through the classical Meyer’s law. The dielectric constant, dielectric loss, and ac conductivity are studied as a function of frequency (100 Hz to 1 MHz) and temperature (313–363 K). All these studies are performed for the first time and aimed to explore the useful and safe region of thermal, mechanical, and electrical properties to enhance effectiveness of PDPHB crystals for device fabrications.

Effect of MoS2 on the tribological properties of in situ Fe3Al-20 wt% Al2O3-4 wt% Cr composites

Fe3Al-20 wt% Al2O3-4 wt% Cr composites containing 0, 5 and 8 wt% MoS2 were subjected to mechanical alloying-inducing self-propagating high temperature synthesis with subsequent hot-pressing sintering. Microstructures of the composites were studied by X-ray diffraction, scanning electron microscopy and energy dispersive spectrum analysis. Then the relative density, room temperature hardness and dry sliding wear behavior of the sintered composites at 25 °C, 500 °C and 800 °C were tested and analyzed. The results showed that composites with different amounts of added MoS2 had good microstructure with high relative density and high hardness. The MoS2 decomposes during sintering with the formation of Fe3Mo3C and Cr2S3. Cr2S3 formed from the decomposition process may form a lubricating film that can decrease the friction coefficient. At 800 °C, Fe3Al-20 wt% Al2O3-4 wt% Cr with 8 wt% added MoS2 exhibited a friction coefficient that was nearly 50% lower than that for the sample with no MoS2 addition. Addition of 8 wt% MoS2 transformed the wear mechanism from adhesive wear to microploughing.

Effect of Ageing at 700 °C on Microstructure and Mechanical Properties of S31042 Heat Resistant Steel

To investigate the effect of high temperature ageing on the microstructure and mechanical properties of S31042 steel, solid solution treatment at 700 °C was carried out for various time from 10 to 6000 h. Experimental results showed that the change of mechanical properties is closely related to the amount of precipitated phases. During ageing from 10 to 300 h, precipitation in the tested steel increases rapidly, and correspondingly, the high temperature yield strength and room temperature hardness of tested steel increase rapidly. Meanwhile, the thickness of the secondary phase on grain boundaries widens sharply and the room temperature Charpy impact absorb energy decreases. Ageing beyond 300 h, the precipitation in the steel increases gradually and the precipitates coarsen to a certain extent. The high temperature yield strength of the steel keeps stable, and the room temperature Charpy impact energy and hardness decrease slowly. Ageing beyond 3000 h, the mechanical properties of the steel tend to be stable. The main precipitates are M23C6, NbCrN and NbC in the tested steel.

The tempering parameter for evaluating softening of hot and warm forging die steels

The tempering characteristics of three different hot and warm forging die steels (FX, 2714, and WF) were systematically studied over a range of temperatures (316–677°C) and a range of times (1–300h). The softening rate for each steel was determined by the change in room temperature hardness. In this study, the hardness data are quantitatively related to the tempering parameter via regression analysis. The tempering parameter (also known as the Hollomon–Jaffe parameter or the Larson–Miller parameter) accounts for the effects of both tempering time and tempering temperature. Room temperature hardness is a measure of the microstructural change that occurs during the tempering process. Results from this study show a bilinear softening as a function of the tempering parameter. For hot and warm forging application the second portion of the curve is more applicable, since these die steels are tempered to some extent before initial use. The slope of the curve can be used as a measure of softening, which is one of the contributing factors on how well the die steel will perform in actual forging operations. These results indicate that WF has the highest resistance to softening during use, FX is somewhat less resistance to softening, and 2714 is the least resistant of the three die steels studied.

Effect of 4wt.% Cr on microstructure, corrosion resistance and tribological properties of Fe3Al–20wt.%Al2O3 composites

Abstract Fe 3 Al–20 wt.%Al 2 O 3 ultrafine grained composites with 4 wt.% Cr were prepared by mechanical alloying inducing self propagating high temperature synthesis with subsequent plasma activated sintering. Microstructures of the composites were studied by X-ray diffraction, scanning electron microscopy, energy dispersive spectrum and transmission electron microscope. Then the relative density, room temperature hardness, static corrosion resistance and dry sliding wear behavior at a temperature range of 25 °C–800 °C of the sintered samples were tested and analyzed. The results showed that the composites had high hardness and a good microstructure with fine grain size, high relative density. The composites with 4 wt.% Cr amount also exhibited excellent comprehensive tribological properties at medium–high temperatures especially at a temperature above 500 °C, although the wear resistance did not be improved at 25 °C–500 °C. 4 wt.% Cr element addition improved the corrosion resistance of the composites significantly with the corrosion loss decreasing by 19.48%.

Characterization of Hybrid Silicon Carbide and Boron Carbide Nanoparticles-Reinforced Aluminum Alloy Composites

Hybrid nanocomposites based on aluminum alloy 6061 reinforced with different hybrid ratios of SiC (0.5, 1.0 and 1.5 vol. %) and B4C (fixed 0.5 vol. %) nanoparticles were successfully fabricated using ultrasonic cavitation based solidification process. The fabricated cast specimens were characterized using SEM study with EDS analysis, hardness test, tension test and impact test. The results indicate that, by the ultrasonic cavitation effects namely transient cavitation and acoustic streaming, the nano reinforcements were successfully incorporated in the aluminum matrix. SEM study with EDS validates the presence of SiC and B4C nanoparticles in the aluminum matrix. Compared to the un-reinforced alloy, the room temperature hardness and tensile strength of the hybrid composites increased quite significantly while the ductility and impact strength reduced marginally. The combination of 1.0 volume percentage SiC and 0.5 volume percentage B4C gives the superior tensile strength. The major reason for an increase in the room-temperature mechanical properties of the hybrid composites should be attributed to the larger hybrid ratio of SiC and B4C nanoparticles, the coefficient of thermal expansion mismatch between matrix and hybrid reinforcements and the dispersive strengthening effects.

Preparation and evaluation of the n-type PbTe based material properties for thermoelectric generators

ABSTRACTOwing to energy conservation of waste heat, Lead telluride, PbTe, based materials have promising good thermoelectric properties around a range of middle temperature (Fig. 1, from 300 to 600°C), due to their high melting point, fine chemical stability, and the high figure of merit Z. The general physical properties and factors affecting the figure of merit have been reviewed. This research is focused on the n-type of PbTe materials and collocated with analysis of densities, hardness, elastic modulus, and thermoelectric properties thermoelectric figure of merit ZT=GS2T/κ (where G is electrical conductivity, S is Seebeck coefficient , T is absolute temperature, and κ is thermal conductivity). Room temperature hardness and Young’s modulus are measured by nano-indentation. In this study, the hot-press compacts under the pressure of 4 ton/cm2 can reach the maximum density about 8.2 g/cm3, and hardness and elastic modulus are 0.6 GPa and 70 GPa, respectively. The figure of merit value (ZT) of PbTe in low temperature (around 340°C) was found about 1 with carrier concentration above 1019 cm−3. These results also indicate that the powder metallurgy parameters provide potentialities for further increase of the high efficiency of energy conversion in PbTe materials.

Quantification of the effect of early microstructural degradation during creep of 9Cr–1Mo–NbV steels at 600 °C

A microstructure-based model for the prediction of the creep resistance at 600°C of 9%Cr steels was applied to literature data, in order to clarify the reasons for the drop in creep strength observed for certain heats of P91 steels. The analysis demonstrated that the observed sigmoidal behaviour of the time to rupture vs. applied stress graph can be explained by the progressive and early dissolution of the fine MX particles which, in the lath interior, interact with dislocations obstructing their mobility. The same phenomenon, whose effects in part eclipse those of the recovery of the substructure, i.e. the lath/subgrain growth and the reduction in free dislocation density, explains the abrupt decrease in the room temperature hardness as measured after rupture with different test durations.

Studies on Dissimilar Welding of AA5083 and AA6061 Alloys by Laser Beam Welding

Dissimilar welds were prepared between 4 mm thick AA5083 and AA6061 sheets using Nd-YAG laser welding with different laser power, beam spot sizes and welding speeds. The results show that the temperature gradient and cooling rates play a major role in resultant microstructures of the weldments. Room temperature hardness and tensile properties of the weldments in the as-welded condition were studied and correlated with the microstructure. The microhardness examination showed that there was significant variation in hardness values at AA6061 side when compared with AA5083 side due to steeper temperature gradient. It has been observed that welds prepared with 3.5kW laser power, 3.5 m/min welding speed and 180 µm beam spot size exhibited highest tensile strength of 241 MPa.

On microstructure and mechanical performance of AlCoCrFeMo0.5Nix high-entropy alloys

A high-entropy alloy system, AlCoCrFeMo0.5Nix, was designed based on the AlCoCrCuFeNi alloy, by replacing Cu with Mo in order to improve strength and thermal stability. Ni content was monitored to see its effect on microstructure and properties. The microstructure of AlCoCrFeMo0.5Nix alloys consists of B2, FCC, and σ phase which are all multi-element solid solutions. As nickel content increases, the constituent phases change from B2 + σ phases at x = 0 to B2 + FCC + σ phases at x = 2.0, reflecting Ni is an FCC stabilizer. The room temperature hardness of the present alloy system decreases from Hv 904 at x = 0 to Hv 404 at x = 2.0. AlCoCrFeMo0.5Nix alloys with x = 0, 0.5, 1.0, and 1.5 exhibit higher hot hardness level than that of Ni-based superalloys, In 718 and In 718 H, up to 1273 K. Furthermore, they possess the less negative value of softening coefficient (BII) at high-temperature regime as compared with those of In 718, In 718 H, and T-800. This superiority can be explained with the slow diffusion rate of vacancies in the multi-element matrix. The present alloy system has great potential in high-temperature applications.

Effect of spark plasma sintering parameters on microstructure and room-temperature hardness and toughness of fine-grained boron carbide (B4C)

Abstract Spark plasma sintering (SPS) parameters are reported to have a remarkable effect on microstructure and fracture toughness of boron carbide. Fully dense fine-grained boron carbide samples have been sintered by SPS at 1700 °C for 3 min as optimal conditions. Both temperature and the current density applied during sintering seem to be important parameters for fully dense output and can induce significant changes on the final microstructure. The initial grain size of the powder is a crucial factor to perform fine-grained fully dense specimens. The improvement on room-temperature hardness and toughness is discussed.

Room temperature elastic moduli and Vickers hardness of hot-pressed LLZO cubic garnet

Cubic garnet Li6.24La3Zr2Al0.24O11.98 (LLZO) is a candidate material for use as an electrolyte in Li–Air and Li–S batteries. The use of LLZO in practical devices will require LLZO to have good mechanical integrity in terms of scratch resistance (hardness) and an adequate stiffness (elastic modulus). In this paper, the powders were fabricated by powder processing of cast ingots. All specimens were then densified via hot pressing. The room temperature elastic moduli (Young’s modulus, shear modulus, bulk modulus, and Poisson’s ratio) and hardness were measured by resonant ultrasound spectroscopy, and Vickers indentation, respectively. For volume fraction porosity, P, the Young’s modulus was 149.8 ± 0.4 GPa (P = 0.03) and 132.6 ± 0.2 GPa (P = 0.06). The mean Vickers hardness was 6.3 ± 0.3 GPa for P = 0.03 and 5.2 ± 0.4 for P = 0.06.