Compressive Creep Strength Research Articles

Effect of Silane Coupling Agent on the Creep Behavior and Mechanical Properties of Carbon Fibers/Acrylonitrile Butadiene Rubber Composites.

In this study, we investigated the effect of the silane coupling agent on the relationship between the surface free energy of carbon fibers (CFs) and the mechanical strength of CFs/acrylonitrile butadiene rubber (NBR) composites. Moreover, the creep behavior of the CF/NBR composites at surface energetic point of view were studied. The specific component of the surface free energy of the carbon fibers was found to increase upon grafting of the silane coupling agent, resulting in an increase in the tensile strength of the CF/NBR composites. On the other hand, the compressive creep strength was found to follow a slightly different trend. These results indicate the possible formation of a complex interpenetrating polymer network depending on the molecular size of the organic functional groups of the silane coupling agent.

Outstanding compressive creep strength in Cr/Ir-codoped (Mo0.85Nb0.15)Si2 crystals with the unique cross-lamellar microstructure

A (Mo0.85Nb0.15)Si2 crystal with an oriented, lamellar, C40/C11b two-phase microstructure is a promising ultrahigh-temperature (UHT) structural material, but its low room-temperature fracture toughness and low high-temperature strength prevent its practical application. As a possibility to overcome these problems, we first found a development of unique “cross-lamellar microstructure”, by the cooping of Cr and Ir. The cross-lamellar microstructure consists of a rod-like C11b-phase grains that extend along a direction perpendicular to the lamellar interface in addition to the C40/C11b fine lamellae. In this study, the effectiveness of the cross-lamellar microstructure for improving the high-temperature creep deformation property, being the most essential for UHT materials, was examined by using the oriented crystals. The creep rate significantly reduced along a loading orientation parallel to the lamellar interface. Furthermore, the degradation in creep strength for other loading orientation that is not parallel to the lamellar interface, which has been a serious problem up to now, was also suppressed. The results demonstrated that the simultaneous improvement of high-temperature creep strength and room temperature fracture toughness can be first accomplished by the development of unique cross-lamellar microstructure, which opens a potential avenue for the development of novel UHT materials as alternatives to existing Ni-based superalloys.

Laser additive manufacturing of iron aluminides strengthened by ordering, borides or coherent Heusler phase

Laser Additive Manufacturing (LAM) is a near-net-shape processing technology well-suited for the production of parts from intermetallic alloys. Three different iron aluminide alloys have been processed by Selective Laser Melting (SLM) and Laser Metal Deposition (LMD). The alloys selected for LAM represent three different strategies for strengthening iron aluminides at high temperatures: Increase of the ordering temperature D03↔B2 (Fe–30Al–10Ti; all compositions in at.%), precipitation of borides (Fe–30Al–5Ti–0.7B) and generation of coherent A2+L21 microstructures (Fe–22Al–5Ti). It is shown that all three alloying strategies established from as-cast alloys can also be realised through both LAM processes, generating defect free and dense (>99.5%) samples. Yield stress and compressive creep strength also match that of the as-cast alloys above 600°C, while at lower temperatures in some cases higher yield stresses are observed. In addition, the yield stress below 600°C may also depend on the building direction and may change after a heat treatment. No general improvement of ductility is observed, specifically in case of Fe–30Al–10Ti, where the grain size in the LAM processed samples is one magnitude lower than in the as-cast alloy. However, depending on building direction and subsequent heat treatment some samples become ductile at quite low temperatures, which at least in some cases may be explained by the internal stresses measured by XRD.

Microstructural Stability and Creep Behavior of Directionally Solidified MgAl<sub>2</sub>O<sub>4</sub>/Y<sub>3</sub>Al<sub>5</sub>O<sub>12</sub> Eutectic Composite

In the present work, compressive creep characteristics of directionally solidified MAS-YAG (MgAl2O4/Y3Al5O12) were investigated at high temperature. The compressive creep strength of a crystal grown at a rate of 5 mm/min and a flow rate of 1.2 mm/min at 1500 °C under a strain rate of 1.0 × 10-4 was only 400 MPa, which is slightly higher than that of crystals grown under different conditions. The compressive creep strength of an oxide eutectic fabricated by the directional solidification method is higher than that of a polycrystalline sintered eutectic with the same composition. The creep behavior at high temperature was studied and the mechanisms of deformation by dislocation motion were revealed by Transmission Electron Microscopy (TEM) observations.

Effect of growth rate on the microstructure and mechanical behavior of directionally solidified Y3Al5O12/MgAl2O4 eutectics

The mechanical properties of YAG–spinel (Y3Al5O12/MgAl2O4) eutectic rods were studied as a function of the solidification rate. Eutectic rods were grown by a laser-heated floating zone method. YAG–spinel eutectic rods measuring 2mm in diameter and 200mm in length were grown at rates of 0.1–10mm/min with a temperature gradient of approximately 1×104K/m. The compressive creep strength of a crystal grown at a rate of 5mm/min and a flow rate of 1.2mm/min at 1500°C under a strain rate of 1.0×10−4 was only 398MPa, which is slightly higher than that of crystals grown under different conditions. The highest flexure strength of the Y3Al5O12/MgAl2O4 material at ambient temperature was obtained at a growth rate of 5mm/min. The maximum hardness reached 16.7GPa, and the room fracture toughness was 3.9MPam1/2. The changes in the mechanical behavior and the microstructure of the material that occurred at different growth rates are briefly discussed.

Microstructure and creep properties of a near-eutectic directionally solidified multiphase Mo–Si–B alloy

Due to their excellent creep behavior and acceptable oxidation resistance at ultrahigh temperatures multiphase Mo-based alloys are potential candidates for applications in aerospace engines and the power generating industry. The resulting materials properties, as well as the microstructure of Mo–Si–B materials, strongly depend on the manufacturing process. In the following paper we report on a new Mo–Si–B alloy which was processed by crucible-free zone melting (ZM) from cold pressed elemental powders. SEM investigations of the zone molten microstructure showed well-aligned arrangements of a three-phase microstructure consisting of a Mo solid solution (MoSS), and the two intermetallic phases Mo3Si and Mo5SiB2. First, high temperature mechanical properties, such as the compressive strength and creep strength at about 1100 °C, were evaluated and compared with a commonly used Ni-based superalloy and a PM processed Mo–Si–B material. In comparison to the PM processed reference alloy, the creep resistance of ZM materials was found to be substantially improved due to the relatively coarse directionally solidified microstructure. Thus, ZM alloys show great potential for applications at targeted application temperatures of around 1200–1300 °C.

Mechanical Properties of the Directionally Solidified Ceramic Eutectic of Al2O3/Al16Ti5O34 Phase Structure

AbstractAl2O3/TiO2 eutectics containing 62–64 wt% Al2O3 were fabricated by a laser floating zone method. Raman spectrometry was used to determine the phase composition. The compressive creep strength of AT36 (Al16Ti5O34/Al2O3) crystal at 1500°C under the strain rate of 1.0 × 10−4 s−1 has 372 MPa, which is about higher than β-Al2TiO5 and β-Al2TiO5/Al2O3 crystals. High-temperature flexural strength, elastic modulus, hardness and fracture toughness of the AT36 crystals were analyzed. The highest flexure strength at ambient temperature was found in the material with 36 wt% TiO2. In addition, we briefly discussed the relationships between microstructure and mechanical properties in AT36 crystal.

Microstructure and mechanical properties of directionally solidified Fe–Al–Nb eutectic

An Fe–26Al–9.5Nb (in at.%) eutectic alloy produced by directional solidification (DS) has been characterised regarding its microstructure and basic mechanical properties and the latter are compared with an as-cast (AC) alloy of about the same composition. The DS alloy exhibits a regular fibrous eutectic Fe 3Al + (Fe,Al) 2Nb (Laves phase) microstructure. By electron backscatter diffraction (EBSD) it was found that the growth directions are <111> for Fe 3Al and <1120> for (Fe,Al) 2Nb. The compressive yield strength and compressive creep strength under constant and step-wise increased load for the DS and AC alloy are compared with each other. During creep testing the DS alloy showed high microstructural stability, i.e. only slight coarsening was observed. At 650 °C the DS alloy exhibits creep properties which are better than for binary Fe–Al alloys and which are comparable to P92, a state-of-the-art steel for steam turbine applications. The alloy showed a low mass gain after long-time creep testing in air indicating a good oxidation resistance.

Microstructure–mechanical properties correlation in siliconized silicon carbide ceramics

The microstructure and high temperature mechanical properties of siliconized silicon carbide ceramics (reaction bonded, reaction formed, and biomorphic SiC) have been investigated. The microstructural differences between these materials have been analyzed. Reaction formed and biomorphic SiC show better, high temperature compressive creep resistance and strength than reaction bonded SiC. Additionally, these two materials show a continuous decrease in the creep rate, which is more pronounced at higher temperature and silicon content. This behavior is explained in detail by using a model of creep controlled by a viscous intergranular phase. The maximum strengths were exhibited by the biomorphic SiC when compressed in the axial direction. The strength of reaction formed SiC is roughly the average between the strength of biomorphic SiC compressed in the axial and radial directions. The dependence of the high temperature compressive strength with the microstructure, and volume fraction of SiC is discussed in terms of the minimum solid area approach.

Microstructure and properties of MoSi 2–MoB and MoSi 2–Mo 5Si 3 molybdenum silicides

MoSi 2-based intermetallics containing different volume fractions of MoB or Mo 5Si 3 were fabricated by hot-pressing MoSi 2, MoB, and Mo 5Si 3 powders in vacuum. Both classes of alloys contained approximately 5 vol.% of dispersed silica phase. Additions of MoB or Mo 5Si 3 caused the average grain size to decrease. The decrease in the grain size was typically accompanied by an increase in flexure strength, a decrease in the room temperature fracture toughness, and a decrease in the hot strength (compressive creep strength) measured around 1200 °C, except when the Mo 5Si 3 effectively became the major phase. Oxidation measurements on the two classes of alloys were carried out in air. Both classes of alloys were protected from oxidation by an in-situ adherent scale that formed on exposure to high temperature. The scale, although not analyzed in detail, is commonly recognized in MoSi 2 containing materials as consisting mostly of SiO 2. The MoB containing materials showed an increase in the scale thickness and the cyclic oxidation rate at 1400 °C when compared with pure MoSi 2. However, in contrast with the pure MoSi 2 material, oxidation at 1400 °C began with a weight loss followed by a weight gain and the formation of the protective silica layer. The Mo 5Si 3 containing materials experienced substantial initial weight losses followed by regions of small weight changes. Overall, the MoB and Mo 5Si 3 additions to MoSi 2 tended to be detrimental for the mechanical and oxidative properties.

The creep and thermal stability characteristics of a unidirectionally solidified Al2O3/YAG eutectic composite

Compressive creep characteristics at 1773, 1873, and 1973 K, oxidation resistance over 1000 h at a temperature of 1973 K in ambient air, and the thermal stability characteristics at 1973 K in ambient air of a unidirectionally solidified Al2O3/YAG eutectic composite were evaluated. At a test temperature of 1873 K and a strain rate of 10−4/s, the compressive creep strength of a eutectic composite manufactured by the unidirectional solidification method is approximately 13 times higher than that of a sintered composite with the same chemical composition. The insite eutectic composite also showed greater thermal stability, with no change in mass after an exposure of 1000 hours at 1973 K in ambient air. The superior high-temperature characteristics are closely related to such factors as (1) the in-situ eutectic composite having a microstructure, in which single crystal Al2O3 and single crystal YAG are three-dimensionally and continuously connected and finely entangled without grain boundaries and (2) no amorphous phase is formed at the interface between the Al2O3 and the YAG phases.

An evaluation of the properties of Cr 3Si alloyed with Mo

The properties of a Cr 3Si alloy designed for the high temperature, high velocity gas flow conditions typical of the operating environment within an aircraft engine are discussed. The alloy composition was obtained by macroalloying Cr 3Si with Mo to improve its high temperature oxidation resistance. Detailed cyclic, isothermal and low temperature “pest” oxidation studies conducted between 773 and 1673 K revealed that the alloy has excellent oxidation properties due to the formation of dual protective oxides scales of Cr 2O 3 at low temperatures and SiO 2 at high temperatures. Preliminary burner rig tests conducted at 1473 K in a 0.3 mach combustion flame indicated that the alloy life is expected to exceed 100 cycles. The alloy exhibits a compressive brittle-to-ductile transition temperature of about 1500 K. The compression strengths vary between 650 MPa at 1500 K and 50 MPa at 1700 K. Preliminary results suggest that the compressive creep strength of the as-cast alloy is equal to or better than MoSi 2-reinforced with either SiC p or SiC w, while that of the powder metallurgically-processed alloy is comparable only to the unreinforced MoSi 2. The room temperature fracture toughness of the alloy was determined to be between 2.0 and 3.0 MPa m 1 2 .

A preliminary assessment of the properties of a chromium silicide alloy for aerospace applications

A preliminary assessment of the physical, mechanical and oxidation properties of a two-phase Cr 3Si alloy macro-alloyed with Mo for potential aerospace applications is discussed. Detailed cyclic, isothermal and low temperature “pest” oxidation studies conducted between 773 and 1773 K revealed that the alloy has excellent oxidation properties due to the formation of dual protective oxides scales of Cr 2O 3 at low temperatures and SiO 2 at high temperatures. The alloy also lasted at least 100 cycles at 1473 K under the action of a 0.3 mach combustion flame in burner rig tests. The compressive brittle-to-ductile transition temperature of the alloy is about 1500 K. The compressive creep strength of the as-cast alloy at 1500 K is as good or better than MoSi 2 reinforced with either SiC p or SiC w, respectively, while those of the powder metallurgically processed alloys are comparable only to the unreinforced MoSi 2. The room temperature fracture toughness of the alloy was determined to be 2.5 MPa m 1 2 .

ＭＡ・ＯＤＳ Ｎｉ基超合金の高温強度

Although it is expected that mechanically alloyed oxide dispersion strengthened (MA·ODS) Ni-base superalloys have enough creep strength at even ultra-high temperature near to solidus, no investigation has been done on it. Accordingly compressive creep strength and stability of dispersoids of MA·ODS Ni-base superalloy, MA 758, at 1523 to 1623K were investigated, and following results were obtained.(1) Steady-state creep rate(es) and stress exponent (n) were different between transverse and longitudinal direction; es of transverse is about one eighteenth of one of longitude, and n of those directions were 6 and 2.1 respectively at 1573K under 15 to 125MPa.(2) Values of apparent activation energy for creep obtained for the transverse and the longitudinal were 115.1 and 133.0kcal/mol respectively which are about twice as large as one of Ni for self diffusion.(3) Fracture modes of creep rupture were also different between the transverse and the longitude; fracture of the former was occured by slipping between longitudinal boundaries of elongated grains and following voids and cracks, the latter took place at grain boundaries under triaxially stressed state caused by buckling of the elongated grains.(4) Mean diameters of dispersoids before and after heating at 1623K (0.986Tm, Tm: solidus) for 200hr were 13.1 and 21.2nm, and the drop of hardness was minimal 6 or 7%, which shows strong stability of them at such a high temperature.

Development of a Die Material for Isothermal Forging of Superalloys in Air

In isothermal forging, since the die is heated as well as the workpiece, high-temperature strength is essentially required for the die material. In particular, isothermal forging of superalloys is carried out at high temperature ranging 1000-1100°C, thus a molybdenum-base alloy, TZM, is generally used as a die material. Although TZM has good high-temperature strength, its oxidation resistance is very poor at above 600°C, therefore, forging must be done in vacuum or inert-gas atmosphere.If there is a die material having both enough strength and oxidation resistance at around 1000-1100°C, isothermal forging of superalloys in air will be possible, and the forging apparatus will be simpler.To develop such a die material, the authors directed their attention to chromium free nickel-base cast alloys, because such alloys are able to contain a large amount of heavy metals such as molybdenum and tungsten, as being soluble in γ and γ' instead of chromium, and are expected to have higher strength at above 1000°C.Several conventional and experimental alloys were investigated. From the results of compression, compressive creep and oxidation resistance tests, “Nimowal” (Ni-10Mo-12W-6Al-0.01Y) showed the best properties as a whole. Its short-time strength is equivalent to that of Mar-M200 at 950-1000°C, higher than that of Mar-M200 and equivalent to that of TZM at 1050-1100°C. Its compressive creep strength is higher than that of Mar-M200 at 1000-1100°C. Oxidation resistance of Nimowal is equivalent to that of Mar-M200 and enough to be used in air. Moreover, JVimowal has better machinability than Mar-M200.Simulation tests of isothermal forging of superalloys in air were made with Nimowal being used as the die material. One-tenth model disk of In-100 was successfully forged from the extruded billet without any damage or significant oxidation of the die.

ＦＲＰのエッジワイズ圧縮破壊特性に及ぼす時間および温度の影響

In order to clarify the mechanism of the effect of specimen diameter on impact strength of FRP in the edge-wise direction obtained by the Hopkinson pressure bar method, the compressive creep tests were perfomed on FRP and polyester resin used as the matrix of FRP and the effects of time and temperature on the compressive properties of these materials were investigated.From the experiments, it was found that the principle of time-temperature superposition was applicable for both the creep compliance of polyester and the compressive creep strength of FRP.Then, a prediction method of the compressive creep strength of FRP was derived based on the law of composite where the visco-elastic properties of the matrix was taken into account. The mechanism of the diameter dependence of the observed impact strength of FRP was explained by the present prediction method.

A scanning transmission electron microscopy study of two dental amalgams

Two fully aged amalgam alloys were examined using a scanning transmission electron microscope both in the transmission and scanning mode. The dispersed type amalgam containing a distribution of silver-copper spheres in addition to the Ag 3Sn powder showed a markedly reduced γ 1 grain size compared to a conventional Ag 3Sn type amalgam. It is suggested that the increased compressive creep strength of the dispersed type material is a direct result of the reduced γ 1 grain size and not due to a dispersion hardening effect from the cores of the remaining Ag-Cu spheres. Similarly, the formation of complex Cu-Sn intermediate phases at the Ag-Cu sphere surfaces are unlikely to lead to a dispersion strengthening effect. It is postulated that the reduced grain size in high copper amalgams is a consequence of the enhanced nucleating effect of a copper based phase on γ 1