Temperature Tensile Elongation Research Articles

Microstructure characteristics of high strength-ductility powder metallurgy superalloy hot oscillatory pressed at sub-solvus temperatures

The early high-strength powder metallurgy superalloys used in aero engine are always prepared by hot isostatic pressing (HIPing) at sub-solvus temperature, but the as-HIPed materials experience prior particle boundaries (PPBs), thus the mechanical ductility is reduced. In order to eliminate the PPBs and obtain high ductility, the samples are fabricated by hot oscillatory pressing (HOPing). Microstructures of the samples are characterized by electron back scattering diffraction (EBSD), scanning electron microscopy (SEM) and so on. The results show that compared with hot pressed (HPed) samples, the HOPed samples present higher density, smaller grain size, lower PPBs scale, and enhanced room temperature tensile properties. The room temperature tensile strength and elongation at break of HOPed sample are 1417 MPa and 32.5 %, respectively, which is obviously better than those of HPed sample (1289 MPa and 20.3 %) and those of HIP sample (1363 MPa and 28.5 %). High strength-ductility is attributed to the accelerated densification and the inhibited PPBs induced by the oscillatory pressure.

Grain refinement and mechanical property of Al-Cu-Mg-Si-Ti-Sc alloy in the state of deformation treatment condition

Al-Cu-Mg-Si-Ti-Sc compound metal with distinct content of Sc increment was prepared by using metallurgical engineering processing. The formation of Sc in Al-4.5%Cu-1.3%Mg-0.6%Si-0.2%Ti-xSc compound metal and its microstructural observation was studied with SEM. The mechanical performances of the compound metal were measured by tensile and fatigue tests in the state of machining distortion conditions. The result reveals that the increment of 0.2% rare earth Sc can fine Al-Cu-Mg-Si-Ti-Sc compound metal grain crystals, which enhances ordinary temperature tensile strength, yield strength, and elongation. The low cycle fatigue of Al-5.2Mg-0.8Si-0.25Cr-0.1Zr-0.2Sc compound metal reveals a cyclic steady state, which mainly relies on the amplitude of the density of movable dislocations and gross applied strain during cyclic distortion. Meanwhile, under external action, the dislocation slip is more in-homogeneous, and materials are more prone to trans-granular crack in which grain crystals can coordinate distortion.

Low-cycle Fatigue Behavior and Microscopic Morphology of Fatigue Crack Structure of Al-Cu-Ag-Fe-Mg-Zr-Er Alloy in The Aging Treatment

Al-Cu-Ag-Fe-Mg-Zr-Er alloy with different content of Er addition was prepared by using metallurgy processing. The Al-4.5%Cu-0.5%Ag-0.35%Fe-0.38%Mg-0.1%Zr-xEr alloy phase and its refinement mechanism were studied with SEM. Tensile and fatigue tests were performed for the alloy in the state of deformation treatment condition. The microstructural observations reveal that the addition of 0.2% rare earth Er can effectively refine the grain structure of Al-Cu-Ag-Fe-Mg-Zr-Er alloy. It improves room temperature tensile strength, yield strength, and elongation at break. Under the condition of low cycle fatigue loading, Al-4.5%Cu-0.5%Ag-0.35%Fe-0.38%Mg-0.1%Zr-0.2%Er alloy shows a cyclic strain hardening in the cyclic stress response curves, which mainly depends on forming complex dislocation configurations. The accumulation of slip bands at the front of the grain boundary will lead to intergranular fracture of the material.

Effect of Mn Content on the Toughness and Plasticity of Hot-Rolled High-Carbon Medium Manganese Steel

The tensile and impact deformation behavior of three different Mn content test steels, xMn-1.0C-0.25V-1.5Cr-0.3Mo (5, 8 and 13 wt%), were investigated using mechanical properties testing, SEM-EBSD and TEM. The elongation and -20 °C impact energy of the three types of Mn content test steels increased as the Mn content increased. The room temperature tensile elongation was 9%, 23% and 81%, and the -20 °C impact energy was 9 J, 99 J and 241 J, respectively. The fracture morphologies of 5 Mn and 8 Mn were found to be cleavage fractures with secondary cracks and micro-voids. The 13 Mn fracture morphology was a plastic fracture with many coarse dimples. Transverse cracks perpendicular to the tensile direction occurred on the surface of the gauge area of 5 Mn and 8 Mn tensile specimens, reducing plasticity dramatically. This was mainly related to the martensitic transformation produced by stress. We characterized the martensite near the tensile fracture and speculated the main mode of crack propagation. Furthermore, a little amount of sharp-shaped BCC phase was found in the 5 Mn, which was determined to be a hard phase relative to the austenite matrix by nanoindentation test. These steels have stacking fault energies ranging from ~15 to ~29 mJ/m2 with increasing Mn content 13 Mn has high stacking fault energy (SFE) and austenite stability. Twin-induced plasticity (TWIP) was the deformation mechanism.

The Microstructure, Mechanical Properties, and Corrosion Resistance of a Novel Extruded Titanium Alloy

Titanium alloys are widely used in marine engineering and other industries. To broaden their application, a novel (α + β) titanium alloy Ti−6Al−3Mo−2Zr−2Fe was studied in this work. A tube with an outer diameter of 60mm, inner diameter of 38 mm, and length of 500 mm was produced by ingot metallurgy and hot extrusion. The microstructure, mechanical properties, and corrosion resistance of the tube were systematically analyzed. The as−extruded Ti−6Al−3Mo−2Zr−2Fe alloy exhibited a typical duplex microstructure. EBSD observation showed that a strong <10 1¯0>//RD fiber texture of an α phase with a close−packed hexagonal structure was formed in the radial direction. The transformation temperature Tβ was determined to be 880–890 °C. A duplex microstructure with fine α platelets was obtained when the alloy was solution−treated at 850 °C for 1 h and underwent an aging treatment at 550 °C for 6 h. The room−temperature tensile strength and elongation of the aged alloy reached 1081.5 MPa and 6.5%, respectively. The corrosion resistance was tested by open circuit potential and a potentiodynamic polarization curve. The results show that the corrosion resistance of the Ti−6Al−3Mo−2Zr−2Fe alloy was better than that of the commonly used TC4 alloy in both a 3.5% NaCl solution and an acidic solution.

The effect of PP contamination in recycled high-density polyethylene (rPE-HD) from post-consumer bottle waste and their compatibilization with olefin block copolymer (OBC)

Polypropylene (PP) and Polyethylene (PE) are widely used commodity plastics in packaging industry such as detergent bottles. To produce plastic detergent bottles, very often extrusion blown molded PE-HD as a body and injection molded PP as a screw cap are used. Separation of individual polymer type is difficult due to the similar density. Unfortunately, the melt blending of recycled post-consumer detergent bottle waste leads to deterioration of mechanical properties. Additionally, the percentage of rPP contamination in recycled PE-HD (rPE-HD) from post-consumer bottle waste can be varied depending on local waste composition and different sorting quality. This work investigates the effect of various contamination scenarios with different percentage of rPP from bottle caps in rPE-HD from bottle waste as well as their compatibilization with olefin block copolymer (OBC) on mechanical, thermal, and rheological properties. Moreover, the low temperature tensile properties of blends with OBC are also investigated in this study. The results showed that the increasing rPP contamination leads to deteriorating elongation at break and tensile impact strength. Furthermore, the addition of OBC as a compatibilizer into worse-case contamination scenario (15 wt% rPP in rPE-HD) significantly improved elongation at break and tensile impact strength. Scanning electron microscopy (SEM) confirms the improvement in adhesion between rPP and rPE-HD from recycled bottle waste with the addition of OBC as a compatibilizer. Rheological measurements reveal the interfacial interaction among rPP, rPE-HD and OBC. The low temperature tensile test demonstrated that the addition of OBC as a compatibilizer improved low temperature tensile elongation at break.

Seeded growth of Ti–46Al–8Nb polysynthetically twinned crystals with an ultra-high elongation

Large size polysynthetically twinned crystals of Ti–46Al–8Nb alloy with a parallel lamellar microstructure were successfully prepared using a Ti–43Al–3Si seed by our new operation. A large amount of columnar B2 phase paralleling to the growth direction was found in the final lamellar microstructure. Higher growth rate (>30 mm/h) led to the failure of seeding process. Based on these results, a new mechanism is proposed to describe the seeding process of the hypo-peritectic TiAl alloys. The peritectic α phase is suggested to directly nucleate from the melt, and then act as nucleus for transformed α phase in the subsequent β to α transformation. At the higher growth rate, the appearance of β phase secondary dendrites and homogeneous nucleation lead to the failure of seeding process. High Nb addition leads to a large amount of residual β phase, and these β dendrites finally evolve into B2 phase. The room temperature tensile elongation was measured to be 11.9–18.5% for Ti–46Al–8Nb PST crystals, which is the highest ever reported value for TiAl based alloys.

Effects of Mo segregation on Charpy absorbed energy in Ti-12Mo alloys

Beta phase stabilizing elements such as Mo have strong tendency to segregate. We have introduced swirly type segregation of Mo in Ti-12Mo (mass %) alloy through groove bar rolling. After solution treatment and low temperature aging, hard omega phase was precipitated heterogeneously, which improved the room temperature tensile elongation values without sacrificing tensile strength. In this study, the effect of Mo segregation and heterogeneous distribution of omega phase on Charpy absorbed energy was investigated in Ti-12Mo alloy. Samples with two types of segregation were prepared; namely, swirly segregation in bar rolled sample and layered segregation in plate rolled sample. For comparison, we have also prepared Ti-12Mo bar samples with lesser Mo segregation, through high temperature thermomechanical treatment. Charpy impact tests were carried out at room temperature, 373 K and 473 K, respectively, using the samples after aging to introduce isothermal omega-phase. The samples with the segregation exhibited higher Charpy absorbed energy, especially at higher temperature of 473 K, while the sample with the swirly segregation showed higher Charpy absorbed energy than that with the layered segregation. The sample with lesser Mo segregation exhibited brittle intergranular fracture surface after Charpy testing. On the contrary, samples with Mo segregation exhibited ductile transgranular fracture surfaces.

Effect of α<sub>2</sub> Precipitation on Creep and Tensile Properties of Ga-Added Near-α Titanium Alloys

The effect of α2 precipitation on the creep and tensile properties was investigated for bimodal and lamellar microstructures in two Ga-added near-α Ti alloys with Al equivalences of 10.6 and 11.5. Fine α2 phase formed in the α phase of both alloys. The volume fraction of the α2 phase for the Al equivalences of 10.6 and 11.5 is equivalent to 57.6 % and 73.3 %, respectively, in the binary Ti-Al system at 600 °C. Creep tests were carried out under a constant stress of 310 MPa at 600 °C and tensile tests were performed at room temperature. Lamellar microstructure showed lower minimum creep strain rates than bimodal microstructure for both alloys. The increase in Al equivalence increased creep life by a factor of 1.6 and decreased the minimum creep strain rate from 6.51 × 10-8 s-1 to 3.99 × 10-8 s-1 in bimodal microstructure. In addition, the increase in Al equivalence decreased room temperature tensile elongation although both alloys contained a similar volume fraction of equiaxed α in a bimodal microstructure.

Study on microstructure and strengthening mechanism of AZ91-Y magnesium alloy

AZ91-Y magnesium alloy with different thicknesses were prepared by die casting process. The main existence forms of Y in alloy and the effects of Y on microstructure and mechanical properties of alloy were studied, the main reason for the change of mechanical properties and fracture mechanism were analyzed. The results show that, yttrium exists mainly in the forms of Al2Y phase and trace solid solution in α-Mg. Yttrium can refine the grain of α-Mg, reduce the amount of eutectic β-Mg17Al12 phase and promote its discrete distribution. The room temperature tensile strength and elongation of alloy increased first and then decreased with the increase of Y content. The designed alloys containing 0.6% Y (measured containing 0.63% Y) have better mechanical properties. The change of mechanical properties of alloy is a comprehensive reflection of the effect of solid solution, grain refinement and second phase. The cracking of Al2Y phase and β-Mg17Al12 phase and crack propagation through Al2Y phase and β-Mg17Al12 phase are the main fracture mechanism of magnesium alloy containing yttrium. The cooling rate does not change the trend of the influence of Y, but affects the degree of influence of Y.

Performance Analysis of the Joint Sealing Materials for the Cement Concrete Pavements in Civil Airports

Cement concrete pavements in airfields need to be sealed with all kinds of sealants to prevent the ingress of water or incompressible materials into their joints. Airfield cement concrete pavements have unique in-service conditions, and the sealants in these environments are not only exposed to climatic effects and heavy traffic loads but also to jet fuel and fluids. By analyzing the causes of damage and selecting four types of typical joint sealing materials for cement concrete pavements in civil airports (e.g., silicone, polyurethane, polysulfide, and polythiourethane), the basic physical properties, adhesion, and resistance of these materials are tested. By combining the experimental results with the relevant technical specifications and standards at home and abroad, these materials are divided into high elastic modulus and low elastic modulus based on 23℃ tensile modulus. The surface drying time, cone penetration, elastic recovery rate, tensile modulus, low temperature tensile elongation, tensile bond, fuel immersion characteristics, resistance to heat ageing, and flame resistant properties of these materials are used as performance indices and provide a technical reference for the construction of airport cement concrete pavements.

The Effect of Solution Treatment Temperature on Plastic Deformation and Fracture Mechanisms of Beta-Titanium Alloy

The beta-titanium alloys are used mainly in bioapplications for artificial joints and other implants. They posses interesting properties such as, high corrosion resistance, low Young’s modulus, good plasticity or superelasticity etc. In this work the effect of solution treatment temperature on deformation and fracture properties has been studied. The alloy Ti-35Nb-2Zr was processed via powder metallurgy process (cold isostatic pressing, sintering and subsequent swaging). Swaged alloy was annealed at 800, 850, 900, 950 and 1000 °C. Tensile tests have been performed on such heat treated specimens and the fracture surface has been studied in correlation with microstructure. With increasing annealing temperature both tensile strength (from 925 MPa to 990 MPa) and elongation (from 13 to 25 %) increased where the maximum values were obtained for 900 °C annealed specimens and subsequently slight decrease has been observed. The simultaneous increase of strength and elongation was attached to change of deformation mechanisms which was described by studying fracture surfaces and microstructure of deformed (tensile tested) specimens.

Effects of processing routes on room temperature tensile strength and elongation for Inconel 718

For oil and gas industrial applications, materials of deep downhole drilling components are required to possess tensile strength over 1400MPa at room temperature. The present study demonstrates that processing design for Inconel 718 can widen the spectrum of its mechanical properties to meet the demand for ultra-high room temperature tensile strength. The range of room temperature tensile properties achieved in this study include tensile strength of 1785MPa in one end of spectrum, and large tensile strain over 40% in the other end. Furthermore, a well-balanced tensile property of 1430MPa with 18% tensile strain can be achieved by minimizing the formation of pre-aging δ precipitates through direct aging process. The strengthening mechanisms and the trade-off between tensile strength and ductility have been investigated and discussed.

Influence of Heat Treatment on the Microstructures and Mechanical Properties of K465 Superalloy

The microstructures and mechanical properties of superalloy K465 under different heat treatment, including as as-cast, solution treatment and aging, were investigated. The results showed that γ' precipitates in as-cast condition exhibited two kinds of morphologies of fine regular cuboidal shape at dendritic arm and coarse irregular form in interdendritic region. MC carbides decomposed into M6C carbides partly after 1210°C/4h solution treatment. The high temperature stress-rupture life can be improved obviously with the increasing cooling rate. When cooling rate was lower than 70°C/min, the room temperature tensile elongation increased with cooling rate increasing. When cooling rate was higher than 90°C/min the room temperature tensile elongation decreased with cooling rate increasing. The proper cooling rate of 70oC/min~90oC/min is advantageous for the achievement of excellent comprehensive properties. When aging treatments continued the regularization of γ' resulted in the improvement of stress-rupture life and the reduction of tensile elongation. The mechanical property gap between the solution treatment and aging can be decreased with increasing cooling rate.

Development of Al-Mg Alloys with Different Levels of Mn and Fe for Super-Plastic Forming

New Al-Mg alloys have been developed for super-plastic forming (SPF) based on commercial AA5083/AA5086 alloys, but with an increased Mn content from 0.5 to 1.5 wt.% and a decreased impurity Fe level from 0.25 to 0.05 wt.%.The effects of Mn and Fe levels on super-plasticity have been investigated by high temperature tensile testing of cold rolled H18 sheets at 425 to 525°C with a strain rate of 2×10-3 s-1. The microstructure evolution during different processing stages, grain size and grain size stability were investigated by optical microscopy and scanning electron microscopy. Both Mn and Fe showed a similar and significant contribution to grain size control in recrystallization, but their effect on high temperature sheet formability was different. An increase in Mn level led to an improvement in high temperature tensile elongation, while an increase in Fe content reduced the sheet formability. A new alloy with 1.5 wt.% Mn and 0.05 wt.% Fe, when processed to H18 temper, was able to reach more than 400% tensile elongation at 450 - 500°C with a strain rate of 2×10-3 s-1.

Microstructure and mechanical properties of Fe–7Al based lightweight steel containing carbon

The effect of carbon on the microstructure and mechanical properties of lightweight steel based on Fe–7 wt-%Al produced by air induction melting with flux cover is investigated. The ingots were hot worked to plates and were characterised. Steel containing 0.02 wt-%C exhibited a single phase microstructure Fe–Al(α), whereas steel containing 0.5 and 1.0 wt-% carbon exhibited a two-phase microstructure containing significant amounts of Fe3AlC0.5 precipitates in Fe–Al(α) matrix. Microhardness of the matrix decreases with increasing carbon content due to depletion of aluminium from the matrix to form Fe3AlC0.5 carbides. The bulk hardness, room temperature strength increases and tensile elongation decreases with increasing carbon content. However, at 873 K the improvement in strength as well as creep properties with increasing carbon content is marginal.

Ultrafine-grained structure formation in Ti-6Al-4V alloy via warm swaging

The influence of warm swaging on the structure and properties of Ti-6Al-4V alloy was studied. Warm swaging of the alloy in the interval 680-500°C with the total strain of ε=2.66 was found to be resulted in the formation of a homogeneous globular microstructure with a grain size of 0.4 μm in both longitudinal and transversal sections. Room temperature tensile strength and tensile elongation of the swaged alloy was 1315MPa and 10.5%, respectively. Ultrafine-grained Ti-6Al-4V alloy produced by swaging exhibited good workability at 600-700 °C.

Titanium Alloy Developments For Future Fan Disc Applications – The Fatigue Response of <i>“Alloy 104”</i>

Alloy 104 is a novel high strength, α+β titanium alloy primarily aimed at aero-engine fan disc applications. Two microstructural variants of Alloy 104 have been assessed. Room temperature tensile strength and elongation have been investigated alongside a more detailed study of low and high cycle fatigue behaviour. The alloy clearly demonstrated an improved fatigue resistance in both microstructural conditions, whilst maintaining forgeability and a comparable density to Ti-6Al-4V. Furthermore, the alloy has been subjected to a load regime with a hold period at peak loads and proven to be insensitive to dwell fatigue.

The Effects of Rolling Process on the Microstructure and Properties of Columnar-Grained Cu-12 Wt%Al Alloys

Cu-12 wt.%Al (Cu-12Al) alloy fabricated by continuous unidirectional solidification (CUS) process has high elasticity, high strength, high conductivity, high plasticity and other good comprehensive properties, which has a potential to develop into a high-performance elastic material as the alternative to beryllium bronze. Especially, the room temperature tensile elongation of the columnar-grained structure (CGS) Cu-12Al alloy with high <001>β orientation along the axial direction exceeded 20%, which is six times more than that of the ordinary polycrystalline structure (OPS) Cu-12Al alloy (ε=2-4%) fabricated by traditional casting. The CGS Cu-12Al alloy shows lower flow stress and work-hardening rate during plastic deformation, which determines a dramatic improvement of workability comparing with the OPS alloy. In the present paper, both the effects of the rolling process and its parameters on the microstructure and properties of the CGS Cu-12Al alloy sheets were investigated. The results showed that the CGS sheets (σb=310 MPa, ε=19%) have the maximum reduction of 80% and remain columnar-grained structure after the first rolling pass at 700. After deformation the tensile strength was 401 MPa and the tensile elongation approached to 14%. Then, the hot rolled sheets were rolled again through the second pass at 325 and 700, respectively. The maximum reduction of CGS sheets at 325 warm rolling was 20%, the sheets remain columnar-grained structure and β1'α1' martensitic phase transformation occured; The second pass hot-rolling at 700 showed that the maximum reduction exceeded 60%, and the recrystallization occured in the sheets. After two passes of hot-rolling (total deformation was 92%), although the recrystallization occured, the CGS sheets remained columnar-grained structure (CGS) high tensile elongation (8.3%), which is two times more than that of the as-cast OPS sheets, and is five times as much as the OPS sheets with the same total deformation.

Microstructure and Tensile Property of NiAl-Cr Alloyed with Zr

The microstructure of as-cast NiAl-33.5Cr-0.5Zr alloy is the eutectic colonies of NiAl and Cr phase with non-continuous Heusler (Ni2AlZr) phase segregating at the cell boundaries. After hot isostatic press (HIP) processing at 1573K, 100MPa for 2h, the Ni2AlZr phase changes into Zr-rich phase. The elevated temperature tensile strength and elongation of the HIP-ed alloy are much higher than those of as-cast alloy. It was noted that this alloy either as-cast or HIP processing exhibits a brittle to ductile transition behavior, which is difference between as-cast and HIP-ed alloy. HIP processing decreases the BDTT of the alloy, especially in high strain rates, and lower the range of BDTT. When the strain rate increases by two orders of magnitude, the BDTT has an approximate increase from150K for as-cast alloy to 100K for HIP-ed alloy. The mechanism responsible for elevated temperature deformation has also been discussed.