High Temperature Tensile Strength Research Articles

Microstructural evolution during high-temperature exposure in a thixocast magnesium alloy

The microstructure of a thixoformed AZ91 (Mg–Al–Zn system) alloy was investigated by different techniques after various heat-treatment conditions. The material, supplied in the as-thixocast state, consisted of large α globules separated by a quasi-eutectic phase (α+β). The alloy was exposed to high temperature (395, 415 and 435 °C) for different times to assess its response. Optical metallography showed that the α-Mg-based areas developed into individual grains, whereas β-phase (Mg 17Al 12) particles were present only in the eutectic area of the base material. The eutectic was found on grain boundaries and α-Mg-based grains became enriched in aluminium and zinc due to simultaneous β-phase dissolution and reduction in the amount of eutectic quantity. Static precipitation and/or dissolution were studied at the three treatment temperatures by TEM. A comprehensive study of precipitate evolution at temperatures very close to the solution is relevant because this thixocast magnesium alloy exhibits a good combination of high-temperature tensile strength and ductility in that temperature range.

Intermetallic Alloys Based on Orthorhombic Titanium Aluminide

Orthorhombic titanium aluminides represent the youngest class of alloys emerging out of the group of titanium aluminides. These new materials are based on the ordered orthorhombic phase Ti 2 AlNb, which was discovered for the first time in the late 1980s as a constituent in a Ti 3 Al-base alloy. In the 1990s primarily simple ternary Ti-Al-Nb orthorhombic alloys were investigated in countries such as the US, UK, India, France, Japan, and Germany. The drive was mainly provided by jet engine manufacturers and related research labs looking for a damage-tolerant, high-temperature, light-weight material. This follows the aim of further extending the use of lower density titanium-base materials in temperature regimes, where heavy nickel-base superalloys are the only alternative today. The present understanding of microstructure-property relationships for orthorhombic titanium aluminides reveals an attractive combination of low and high temperature loading capabilities. These involve high room-temperature ductility and good formability, high specific elevated temperature tensile and fatigue strength, reasonable room-temperature fracture toughness and crack growth behavior, good creep, oxidation, and ignition resistance combined with a low thermal expansion coefficient. This article reviews the aspects of composition-microstructure-property relationships in comparison to near-a titanium, TiAl, and nickel-base alloys. Special emphasis is also placed on the environmental degradation of the mechanical properties.

Fabrication of high-temperature resistant oxide ceramic matrix composites

Abstract The main objectives of this work are to develop and apply new ceramic matrix materials by which a relatively high level of densification of the final composite may be achieved by pressureless-sintering at temperatures close to 1200°C. A cost-effective processing method for the production of oxide/oxide CMCs materials and components has been achieved. A range of interphase materials is applied to Nextel™ 720 fibres. These include zirconia, neodymium and lanthanum phosphate. A combination of ZrO 2 and the AKP50 alumina powder have been selected as the successful candidates for the interphase and the matrix material, respectively. Work has been conducted on the preparation of slurry systems consisting of these two materials. The prime target was to establish the possibility of achieving good coating around the bulk of the fibres together with a high level of impregnation with the matrix material. Furthermore, the pressure infiltration technique has been applied and as a result composite samples with fibre volume content of 40%, and remaining porosity of around 20 vol% have been routinely produced. Composite room and high-temperature tensile strengths of around 200 MPa have been accomplished.

The effects of tungsten addition on the microstructural stability of 9Cr–Mo Steels

The effects of tungsten addition on the microstructure and high-temperature tensile strength of 9Cr–Mo steels have been investigated by using three different steels: M10 (9Cr–1Mo), W18 (9Cr–0.5Mo–1.8W), and W27 (9Cr–0.1Mo–2.7W) steels. The tungsten-added 9Cr steels have revealed better high-temperature tensile strength. Microchemical analysis for (Cr,Fe) 2 (C,N) revealed that the tungsten addition increased the Cr/Fe ratio, which resulted in the lattice expansion of (Cr,Fe) 2 (C,N), and then the enhanced pinning effect on the glide of dislocation. In addition, in M10 steel, the M 23C 6 carbides quickly grew and agglomerated, while the tungsten-added 9Cr steels revealed a fine and uniform distribution of M 23C 6 carbides. Dislocation recovery during tempering treatments was delayed in tungsten-added 9Cr steels, which was correlated with the stabilized precipitates and the decreased self-diffusivity of iron. It is, thus, believed that the excellent high-temperature tensile strength of tungsten-added 9Cr steels is attributed to the stabilized M 2X carbo-nitrides and M 23C 6 carbides and the decreased self-diffusivity of iron.

Study on the Initial Torque Characteristics of Friction Welding.

The torque variation during friction welding is related closely to the friction welding mechanism and the mechanical characteristics of the weld. Especially, the influence of initial torque on the accuracy of welded specimen is remarkably high. In this report, the effects of the initial torque characteristics on the friction welding of carbon steel are examined both theoretically and experimentally. The surface roughness of turned surfaces is modeled as triangular columns that are constructed in concentric configuration. Based on the relationship between the temperature change measurements during friction welding and the high temperature tensile strength of carbon steels, the contact width changes of the interrace and the torque changes are estimated. The experimental and theoretical results show good agreement.

How fast can we cast?

Cast productivity depends on casting speed. Since the early development of continuous casting, numerous attempts have been made at high speed casting. With regard to speed limitation by shell sticking, high temperature tensile strength properties of the solidifying shell in relation to mould friction are considered the governing factor. Hence, experimental work has been carried out to simulate shell loading under casting conditions, determining the shell strength for a wide range of carbon contents. Mould friction data have been derived from published plant measurements. As demonstrated, neither shell strength nor mould friction imposes significant limits on casting speed under regular casting conditions.

Heat Resistance of Mg-Zn-Al-Ca Alloy Castings

New Mg-Zn-Al-Ca based alloys are evaluated for possible application at elevated temperatures. The as-cast microstructures of these alloys show that the amount of eutectic compounds increases with an increase in Zn+Al content, and the compounds are found to be mainly Mg 32 (Al,Zn) 49 or MgZn. High temperature tensile strength and 0.2% proof strength increase with an increase in the amount of compounds. The creep properties of the alloys are far superior to those of conventional die-cast AZ91D alloy. However, the presence of soft Mg 17 Al 12 compound deteriorates the creep properties of high Al containing alloys.

Strain Measurement of a Ductile Composite Al<sub>2</sub>O<sub>3</sub>/Y<sub>3</sub>Al<sub>5</sub>O<sub>12</sub> (YAG) by Neutron Diffraction

Strain measurement of an unidirectionally solidified single-crystal Al 2 O 3 / single-crystal Y 3 Al 5 O 12 (YAG) eutectic composite was performed by neutron diffraction technique using two-axis crystal diffractometer with one-dimensional position sensitive detector. Microstructure of this composite shows a formation of a compatible interface with no amorphous phase region among the two-phase grain boundaries. This fact causes excellent characteristics on high-temperature tensile and flexural strengths in the range of 350 ∼ 400 MPa from the room temperature up to 2073 K (just below its melting point of about 2100 K) with no apparent temperature dependence. The neutron diffraction measurements were carried out to measure residual strains of the two phases in the composite, together with the sintered specimens of Al 2 O 3 and YAG as the reference materials, respectively. The YAG phase strains for three crystal lattice planes were successfully evaluated from the full set of the diffraction data. But the corresponding strains for Al 2 O 3 phase were not determined because the data set of Al 2 O 3 phase was not unambiously obtained due to overlapping of the diffraction profiles from the two phases and/or no clear observation of the corresponding set of the peaks. It is shortly discussed that the overlapped profile results from the compatible interfaces with almost equal lattice spacings of the two phases. Contrary to the case of polycrystalline composites, the strains in this composite indicate a strong anisotropy because of the dual phase single crystal constituents.

Phase Stability and High Temperature Tensile Properties of W doped gamma-TiAl

ABSTRACTTungsten (W) doped γ-TiAl is one of promising alloys among many other proposed TiAl base alloys, for the purpose of structural applications at elevated temperatures. Ingots of W doped γ-TiAl were produced by plasma arc melting, followed by homogenizing heat treatment and isothermal forging to control their microstructures. The phase stability of W doped γ-TiAl has been studied quantitatively, using the specimens quenched from 1273 K. Equilibrium compositions of consisting phases were analyzed by means of EDS analysis in a TEM. An isothermal cross section of the Ti-Al-W ternary phase diagram at 1273K has been proposed based on the experimental observations. Small amounts of W addition (< 1at%) to Ti-48at%Al cause a phase shift from α2+γ to α2+β+γ, which suggests that W is the strongest β stabilizer among transition metals, such as Cr and Mo. Mechanical property measurements of W doped γ-TiAl show that the high temperature tensile strength has been improved by the W addition. Relationships between the microstructures and the mechanical properties of W doped γ-TiAl have been discussed.

A study of the microstructure of nanocrystalline Al–Ti alloys synthesized by ball milling in a hydrogen atmosphere and hot extrusion

Nanocrystalline Al–Ti alloy powders were produced by reactive ball milling (RBM) in a hydrogen atmosphere and its microstructure consisted of nano-sized Al and nano-sized TiH2. Thermal analysis of as-milled powders showed that the decomposition of TiH2 and the subsequent formation of Al3Ti occurred at 370–480°C. The powder was consolidated by hot extrusion at 500°C. The grain size of as-extruded specimens was about 50–100 nm. The hardness of Al-5 at.%Ti specimens synthesized by RBM and subsequent hot extrusion was 25–75% higher than that of Al-8 wt.%Ti alloys produced by mechanical alloying (MA) in Ar atmosphere and hot extrusion. Room temperature and high temperature (300, 400, 500°C) tensile strength of RBM Al-5 at.%Ti alloys were superior to those of MA Al-8 wt.%Ti alloys. The strength in these alloys appeared to be related to a large extent to the very fine grain size. The ductility of RBM alloys decreased with grain refinement. It is possible that the deterioration in ductility of nanocomposite Al–Ti alloys has to be attributed to the increase of the interface area between Al and Al3Ti and its high energy. SEM fractograph showed that fracture progressed intergranularly.

Effects of Binder on the Mechanical Properties of Preform and MMCs

The effects of binder on the mechanical properties of the preforms and metal matrix composites (MMCs) were studied. Fibers were , HTZ and fibers(Saffil) and binders were organic binder, inorganic binder, polyacrylamide under various PH conditions. Compressive strength of the preform increased with the addition of inorganic binder. The polyacrylamide did not improve the permeability of the preforms. PH of the slurry should be controlled because it affects the viscosity of the slurry. Good preforms were obtained under following conditions : 3 wt% inorganic binder, 0.1 wt% organic binder, 0.1 wt% polyacrylamide and PH 9. Tensile tests of MMCs were conducted at using MTS(100KN USA). Wear tests were conducted under various sliding speeds. High temperature() tensile strengths of Alborex/Saffil/AC8A and HTZ/AC8A are 80% and 75% of the room temperature tensile strengths respectively. The tensile and wear properties of the Alborex/Saffil/AC8A are superior to that of the HTZ/AC8A. The wear behavior of HTZ/AC8A shows more orthotropic characteristic than that of Alborex/Saffil/AC8A.

Creep rupture life prediction of short fiber-reinforced metal matrix composites

The creep rupture life of an Al/Al2O3 composite and its creep behavior were studied. The metal matrix composite was produced by using a squeeze casting technique. High-temperature tensile tests and creep experiments were conducted on a 15 vol pct alumina fiber-reinforced AC2B Al alloy metal matrix composite (MMC). The high-temperature tensile strength of Al/Al2O3 composite is 14 pct higher than that of an AC2B Al alloy. The steady-state creep rate and the creep life were measured. The stress exponent in Norton’s equation and the activation energy were computed. The stress exponents of the AC2B and Al/Al2O3 composites were found to be 4 and 12.3, respectively. The activation energy of the AC2B and Al/Al2O3 composites was found to be 242.74 and 465.35 kJ/mol, respectively. A new equation for predicting creep life was established, which was based on the conservation of the creep strain energy. The theoretical predictions were compared with those of the experiment results, and a good agreement was obtained. It was found that the creep life is inversely proportional to the (n + 1)th power of the applied stress and strain failure energy of creep is conserved. The creep fracture surface, examined by scanning electron microscopy (SEM), showed that the MMC specimen failed in a brittle manner.

Effect of Roll and Rolling Temperatures on Sticking Behavior of Ferritic Stainless Steels.

The sticking behavior of several austenitic and ferritic stainless steels under the hot rolling conditions was examined in detail using a two disk type hot rolling simulator. The sticking of bare metal to roll surfaces was strongly dependent on the high temperature tensile strength and the oxidation resistance of the stainless steel. A steel having higher tensile strength and lower oxidation resistance exhibited better resistance against sticking. The sticking occurred in increasing severity in the order of 430J1L, 436L, 430 and 409L. It was clarified that a high speed steel (HSS) roll was more beneficial to prevent sticking compared to a Hi-Cr roll.

Improvement of Microstructure and Mechanical Properties in TiB<SUB>2</SUB>-Doped TiAl Alloy by Direct Sheet Casting

Direct sheet casting of γTiAl with TiB 2 particle dispersion was made in order to improve the room temperature tensile ductility of the γTiAl sheets without decreasing their high-temperature strength. As a result, fine equiaxed grain microstructure was formed in the TiAl-1 at%TiB 2 sheet with the average grain size of 10 μm, the finest level among the current TiAl ingot specimens in the as-cast bulk condition. The room-temperature ductility was increased to 2.1% with the high-temperature tensile strength kept at the level of 200 MPa in the TiAl-1 at%TiB 2 sheet. This improvement of room-temperature ductility was attributable to the fact that the high oxygen content, i.e. 0.58 at%, of this material was not harmful to the tensile ductility when the oxygen existed in the solid solution of the α 2 fine lamellar phase or in finely distributed oxide particles, fine enough not to cause brittleness to the matrix. From these findings, it is determined that oxygen was not harmful to the ductility of γTiAl when its microstructure containing oxygen was fine enough.

５０８３アルミニウム合金板溶接継手のクリープとクリープ破断

Creep and creep rupture tests were carried out for MIG welded joints of 5083 aluminum alloy plates under an ambient atmosphere at temperatures between 573 and 723 K. Obtained results were compared to those for the base metal. 5083-O plates of 20 mm thickness were welded by high current MIG welding using 5183 filler wire with a single welding pass for each side. Round bar creep specimens were machined out of the welded joints. The welded joints showed nearly the same minimum creep rate as the base metal at 573 K. However, the minimum creep rate of the welded joints was generally lower than that of the base metal at 623 and 673 K. At these temperatures, creep rupture of the welded specimens always occurred in the base metal. In the welded specimens, creep strain is not uniform and the base metal tended to creep preferentially to the weld metal. The Larson-Miller plot of the rupture time of the welded joints coincided with that of the base metal. High temperature tensile strength of welded joints is slightly higher than that of the base metal.

Effect of yttrium addition on mechanical behavior of powder metallurgy TP304 at elevated temperatures

It is well known that oxide dispersion strengthened (ODS) alloys, which are mechanically alloyed with yttria, possess excellent mechanical properties in comparison with conventional ingot metallurgy (IM) materials at elevated temperatures even higher than 1,000 C. However, mechanical alloying may not be desired in view of production cost for the high temperature application where such high strength is not necessarily required. There is not an extensive literature dealing with mechanical properties at above 800 C of the fully dense powder metallurgy (PM) materials without mechanical alloying. In the present study, the melt of TP304 containing yttrium was atomized to form yttria on and in the powder. The effects of such oxide inclusions on high temperature tensile properties and creep rupture strengths are investigated, using TP304 fully dense materials consolidated by hot extrusion.

The balance of mechanical and environmental properties of a multielement niobium-niobium silicide-basedIn Situ composite

This article describes room-temperature and high-temperature mechanical properties, as well as oxidation behavior, of a niobium-niobium silicide basedin situ composite directionally solidified from a Nb-Ti-Hf-Cr-Al-Si alloy. Room-temperature fracture toughness, high-temperature tensile strength (up to 1200 °C), and tensile creep rupture (1100 °C) data are described. The composite shows an excellent balance of high- and low-temperature mechanical properties with promising environmental resistance at temperatures above 1000 °C. The composite microstructures and phase chemistries are also described. Samples were prepared using directional solidification in order to generate an aligned composite of a Nb-based solid solution with Nb3Si- and Nb5Si3-type silicides. The high-temperature mechanical properties and oxidation behavior are also compared with the most recent Ni-based superalloys. This composite represents an excellent basis for the development of advanced Nb-based intermetallic matrix composites that offer improved properties over Ni-based superalloys at temperatures in excess of 1000 °C.

High-Temperature Brazilian Test for Tensile Strength of Metamorphic Limestone

Abstract This technical note presents a low-cost and fast, high-temperature tensile strength test of rocks. A series of splitting tensile strength tests, the so-called Brazilian test, were conducted on metamorphic limestone specimens at high temperature using a special triaxial cell assembly that can sustain a maximum temperature of 315°C. Results of these Brazilian tests at various temperatures (30, 100, 200, and 300°C) are presented and discussed. The results show that the tensile strength of the rock decreases as the temperature of the rock increases. The reduction in tensile strength is found to be greater when the tests are actually conducted at high temperature rather than at room temperature using thermally treated specimens.

Microstructure Control in Iron Aluminides by Phase Decomposition or by Mechanical Alloying for Improved Strength and Ductility

ABSTRACTThe iron aluminides based on Fe3Al or FeAl being developed for intermediate temperature applications suffer from mediocre room temperature strength and ductility and poor high temperature tensile and creep strength. Attempts to overcome these problems have been restricted by the limited possibilities of structure modification by, for example, precipitation of stable strengthening particles. The present study examines two approaches to obtaining two-phase mixtures for improved strength and ductility: by adjusting chemical compositions such that two-phase order-disorder (α-α″) mixtures are obtained, and by mechanical alloying. Two-phase α-α″ mixtures are obtained by heat treatment of Fe-Al alloys with Al content near 20–24% and in ternary Fe-Al-Si alloys with suitably adjusted Al and Si contents. Microstructures of such alloys can be modified during heat treatments by ordering, precipitation or decomposition, and two-phase mixtures similar to those in the γ-γ superalloys obtained. Such two-phase alloys show good high temperature tensile and creep strength with some indication of reasonable ductility and reduced environmental sensitivity. Mechanical alloying can easily produce FeAl alloys of fine grain size reinforced with stable oxide particles. These structures lead to high room temperature strength with some ductility: controlled recrystallization can significantly modify both strength and ductility.

Ductility Improvement of Direct-Cast Gamma TiAl-Based Alloy Sheet

ABSTRACTFor improving the room temperature tensile ductility of direct-cast gamma TiAl sheets without affecting their high-temperature strength, direct sheet casting with T1B2 particle dispersion is employed and conducted. The T1B2 addition and rapid cooling results in the formation of a fine equiaxed grain microstructure with an average grain size of ∼10μm, contributing to the increase in the room temperature ductility to 2.1% with the high-temperature tensile strength kept at about 200MPa. This improvement of room-temperature ductility is attributable to the following fact. The high oxygen content of this material, about 2500wt. ppm, is not harmful to the tensile ductility when the oxygen is in the solid solution of the 0:2 lamellar phase or in oxide particles, which are fine enough not to cause brittleness to the matrix. From these findings, a principle is proposed that oxygen is not harmful to the ductility of gamma TiAl when its microstructure containing oxygen is fine enough.