Temperature Ultimate Tensile Strength Research Articles

Effect of trace boron addition on the microstructural evolution and mechanical properties in Ti45Al8Nb2Cr-B alloys

High Nb-containing TiAl alloys have been deemed ideal candidates for demanding structural applications under high temperatures due to their appealing mechanical qualities and low density. Nonetheless, its inherent brittleness at room temperature remains a significant impediment to its processability. Herein, different concentrations of boron were added into the Ti45Al8Nb2Cr (Ti4582) alloy by vacuum arc melting to tailor the microstructure and corresponding mechanical properties. The coarse lamellar colonies were significantly refined via boron addition, while excessive boron addition did harm to the mechanical properties. The different morphologies of the borides (Bf or B27) profoundly influenced the microstructure and mechanical properties of as-prepared alloys. Further elemental distribution, phase constitution, lamellar colony size, and mechanical properties were systematically investigated. Noteworthily, trace boron additions effectively improved the mechanical properties of Ti4582-xB alloys with an optimal adjustment in Ti4582–0.2B, showing 673 MPa for room temperature ultimate tensile strength (UTS) with elongation of 1.3 % and 1623 MPa for ultimate compressive strength (UCS) with compressive strain of 32.5 %. The improved mechanical properties of Ti4582-xB were mainly attributed to grain refining and second phase strengthening. Moreover, the hindrance and accommodation for dislocations by deformed twins and reinforcements effectively enhanced the mechanical properties.

Characterization of the microstructure, texture, and tensile behavior of additively manufactured Hastelloy X superalloy: Insights into heat treatment at 900 °C

This research aimed at the microstructural characterization and elucidation of room- and high-temperature tensile properties of additively manufactured Hastelloy X Ni-based superalloy heat-treated at 900 °C. The samples were fabricated via the laser powder bed fusion method utilizing two scan strategies known as island and meander types. The results indicated that the cellular structure embedded in the columnar grains of the as-built microstructure disappeared after applying the heat treatment, linking to the reduction in dislocation density while keeping the former morphology of the grains unchanged. However, the intensities of the Brass, Goss, Goss-Brass, and rotated Goss texture components were reduced, leading to the generation of more homogenous fibers in the heat-treated microstructure. Additionally, it caused the formation of a Mo-rich phase on the grain boundaries, which improved the room temperature's ultimate tensile strength. However, it was elucidated that the Mo-rich phase-induced void formation and intergranular cracking failure caused a slight decrease in hot ductility. Overall, the obtained results revealed that the heat-treated island samples showed superior hot tensile behavior than the meander sample due to having a larger grain size.

Multi-stage strain-hardening and nano-twinning strengthening Co40Cr22Ni15Fe14Mo4Si3Mn2 multi-principal element alloy

CoCrNiFe multi-principal element alloy (MPEA) plates were prepared by melting and rolling. Thermomechanical treatment (cold rolling and aging) was developed to modify the formation of lattice defects and precipitates. The results show that the Co40Cr22Ni15Fe14Mo4Si3Mn2 MPEA have excellent room temperature ultimate tensile strength and hardness of 1946 MPa and 684 HV0.1. Electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) techniques were used to reveal the microstructure and provide insight into the mechanism. The strengthening mechanism comes from the multiple factors, and most notably, the interaction between nano-twins and Lomer-Cottrell locks. The presence of nano-twins and stacking faults has a significant impact on the strain hardening behavior of the alloy. At the same time, the occurrence and development of deformation substructure dominated by dislocation configuration is the reasons for the material to achieve multi-stage strain hardening (MSSH). This method of realizing MSSH behavior by adjusting microstructure is of great significance in the design and application of FCC MPEA and can be extended to other FCC alloys.

Effect of high preheating on the microstructure and mechanical properties of high gamma prime Ni-based superalloy manufactured by laser powder bed fusion

Laser powder bed fusion (L-PBF) is an additive manufacturing method with potential applications in the aerospace industry. Currently, IN738LC has been a challenging engineering material to work with as it is inherently brittle due to its high γ′ volume fraction. In this study, crack-free IN738LC was manufactured on a customized L-PBF system capable of preheating to 700 °C. A wide processing parameter range (58–83 J/mm3) could be selected to achieve solid bulk fabrication with a density of 99.95%. The microstructure and mechanical behavior difference between preheating at 200 °C and 700 °C were assessed. In addition to achieving cracking suppression, the high preheating temperature resulted in a strong textured columnar microstructure with finely dispersed carbide particles along the grain boundaries of as-built parts, and superior room temperature ultimate tensile strength of 1612 MPa associated with good ductility of 18% was achieved. Work hardening rate evolution that differed from 200 °C preheating was thought to cause abnormal anisotropic tensile behavior. The influence of preheating on the melt pool morphology, the development of fluid dynamics, and the thermal behavior were discussed according to simulations with the discrete element model (DEM) and volume of fluid (VOF) method.

Laser powder bed fusion of C18150 copper alloy with excellent comprehensive properties

Laser powder bed fusion (LPBF) of copper alloys is expected to revolutionize aerospace propulsion and related industries. This study reports an LPBF-fabricated C18150 copper alloy with excellent comprehensive properties, e.g., thermal conductivity and tensile properties, at both room and elevated temperatures (300 °C, 500 °C). The results show that the nearly full dense specimens are obtained by using optimal process parameters. The microstructure of both the as-built (AB) specimens and the direct aging (DA) specimens at different aging temperatures (480 °C, 530 °C, and 580 °C) with a constant aging time of 4 h mainly consisted of columnar grains, and the grain size remains almost unchanged after aging treatment. The Cr precipitates grow and aggregate with the increase in the aging temperature. The highest room temperature ultimate tensile strength (UTS) of 501 MPa is obtained for specimens aged at 480 °C due to the strong precipitation strengthening effect induced by the tiny and dispersed Cr nano-precipitates. The specimens aging at 580 °C show the highest thermal conductivity of 313 W m−1 K−1 due to the recovery of lattice distortion induced by the Cr atoms dissolution. The trends in tensile properties and thermal conductivity of samples tested at 300 °C are consistent with those at room temperature. When the test temperature is 500 °C, the AB specimens achieve the highest UTS of 274 MPa and thermal conductivity of 259 W m−1 K−1 due to the in-situ precipitation of Cr atoms. This work introduces LPBF C18150 specimens with excellent comprehensive properties and promotes the application of LPBF copper alloys in the industry at different service temperatures.

Effect of post process shear straining on structure and mechanical properties of 316 L stainless steel manufactured via powder bed fusion

Powder Bed Fusion (PBF) has become popular despite the fact that PBF-prepared components feature characteristic defects. Their performance, however, can be shifted to the next level by the application of post-processing, advantageously via intensive plastic deformation. The study characterizes the effects of rotary swaging performed at hot, cold, and cryogenic conditions on the (sub)structure and mechanical properties of workpieces of AISI 316 L stainless steel, favourably used in constructions as well as medicine, manufactured by PBF. The workpieces built in the horizontal and vertical directions were analysed to assess their structures, residual strain and stress, density, and porosity; porosity was observed primarily in the horizontally built workpiece also featuring lower density and larger average grain size. Subsequently, the workpieces were subjected to rotary swaging, which contributed to (almost) complete elimination of porosity, evident substructure development, and significant grain refinement – the vertically built workpiece exhibited the avg. grain size of 2.3 µm, 1.8 µm, and 0.1 µm after hot, cold, and cryo swaging. The cryo-swaged sample also exhibited specific texture, room temperature ultimate tensile strength (UTS) of more than 2 000 MPa, and two times higher microhardness compared to the as-build workpiece. All the swaged pieces exhibited significantly improved mechanical properties, even at the testing temperature of 900 °C. • rotary swaging reduced/eliminated printing defects of as-printed workpieces. • structure significantly refined, down to ultra-fine-grain level after cryo-swaging. • specific texture contributed to exceptional mechanical behaviour (at elevated temperatures). • combining powder bed fusion plus rotary swaging is a promising prospective production technology.

Precipitation and growth of Laves phase and NbC during aging and its effect on tensile properties of a novel 15Cr–22Ni–1Nb austenitic heat-resistant steel

The microstructure evolution and the mechanical properties of 15Cr–22Ni–1Nb austenitic heat-resistant steel were investigated during the aging up to 24 h at 780 °C, 820 °C and 860 °C. A large amount of Laves phase and nano-sized NbC were precipitated during the aging. The NbC particles exhibit excellent coarsening resistance, and the coarsening rate constant of nano-sized NbC particles is four orders of magnitude smaller than that of Laves phase during the aging at different temperatures. The room temperature tensile strength of the heat-resistant steel after aging at 820 °C for 4 h is highest among different aging treatments. The volume fraction of Laves phase increase with the increase in aging temperature and holding time, resulting in a decrease in the ductility of the heat-resistant steel. Ostwald ripening was observed during the aging for 8 h at different aging temperatures. Consequently, the high temperature ultimate tensile strength of heat-resistant steel after the aging for 8 h is lower than that for 4 h and 24 h. The precipitation strengthening contributed by Laves phase and nano-sized NbC was estimated. The yield strength contributed by submicron Laves phase particles is smaller than that provided by nano-sized NbC particles.

Enhancing strength via nano-lattice defects in La0.008Al0.08FeCoCrNiMn high-entropy alloy produced by rapid solidification, cold rolling and annealing

Multiple lattice defects play a crucial role in improving the mechanical properties of FeCoCrNiMn high entropy alloys (HEAs). In the present work, the strength and hardness of the La0.008Al0.08FeCoCrNiMn HEA were first increased and then decreased during the annealing process due to the competitive mechanism between the recrystallization softening and precipitated phase hardening. Especially, a superior room temperature ultimate tensile strength (1403 MPa) and a fracture strain (9.1%) have been obtained, which was treated by quenching in the liquid metal, cold rolling at room temperature, and annealing at 600 °C for 32 min. The characterizations and analysis indicate that the fundamental cause of the strengthening is attributed to the synergistic effects of nano-sized precipitated particles (mean size: 20.2 nm), dislocation cells, and nano-twins (∼10 nm in thickness) together with Lomer-Cottrell locks. Meanwhile, the effects of different lattice defects on strength contribution have been quantified.

Influence of Temperature on the Mechanical Performance of Unidirectional Carbon Fiber Reinforced Polymer Straps.

The performance of pretensioned, laminated, unidirectional (UD), carbon fiber reinforced polymer (CFRP) straps, that can potentially be used for example as bridge deck suspender cables or prestressed shear reinforcements for reinforced concrete slabs and beams, was investigated at elevated temperatures. This paper aims to elucidate the effects of elevated temperature specifically on the tensile performance of pretensioned, pin-loaded straps. Two types of tests are presented: (1) steady state thermal and (2) transient state thermal. Eight steady-state target temperatures in the range of 24 °C to 600 °C were chosen, based on results from dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). Transient state thermal tests were performed at three sustained tensile load levels, namely 10, 15, and 20 kN, corresponding to 25%, 37%, and 50% of the ultimate tensile strength of the pin-loaded straps at ambient temperature. In general, the straps were able to retain about 50% of their ambient temperature ultimate tensile strength (UTS) at 365 °C.

Microstructure and mechanical properties of an ODS ferritic steel with very low Cr content

An ultra-low Cr oxide dispersion strengthened (ODS) steel with the composition of Fe-5Cr-4.5Al-0.6Zr (hereinafter abbreviated as 5CrAlZr ODS steel) were proposed and manufactured via mechanical alloying (MA) and hot isostatic pressing (HIP), followed by hot forging treatment. TEM results indicate that a large amount of fine δ-Y4Zr3O12 particles were formed within the grains and along the grain boundary, additionally, Y6ZrO11 and Al2Y4O9 nano-particles with larger size were also detected. The mean particles diameter (dp), the mean inter-particle spacing (λ) and number density (nv) of the nano-oxide particles in the 5CrAlZr ODS steel are about 10 nm, 80 nm and 1.23 × 1022 /m3, respectively. The room temperature ultimate tensile strength (UTS) and the total elongation (TE) of the fabricated 5CrAlZr ODS steel are 875 MPa and 21%, respectively, which are higher than those of traditional 5Cr-2W-0.24V steels. The UTS and TE of 5CrAlZr ODS steel at 700°C are 234 MPa and 58%, respectively. The strengthening mechanisms underlying were also discussed.

Microstructure, tensile properties and creep behavior of high-Al TiAlNb alloy using electromagnetic cold crucible continuous casting

Newly designed Ti–47Al–10Nb alloy was prepared at growth rates ranging from 0.3 mm/min to 1 mm/min under power of 45 kW using electromagnetic cold crucible continuous casting technique. The macro/microstructure, tensile properties and creep behavior are studied. Results show that this alloy can be directionally solidified at growth rates from 0.3 mm/min to 0.7 mm/min, and this alloy exhibits the β-solidification at growth rates from 0.3 mm/min to 1 mm/min. The lamellar spacing decreases with the increasing of growth rate, and the relationship between lamellar spacing and growth rate can be fitted by d=371.2V−0.56. The directional solidification structure has little effect on room temperature ultimate tensile strength, and the creep properties strongly depend on the directional solidification structure. At the optimum preparation parameters of 0.5 mm/min and 45 kW, this alloy exhibits the good room-temperature tensile properties with ultimate tensile strength 562 MPa and elongation 1.42%, and the minimum strain rate is 4.31 × 10−8s−1 during creep at 800 °C/200 MPa. Moreover, in directional solidification structure, the plastic incompatibility of lamellar colonies leads to the local stress concentration at the steps of vertical colony boundary, which promotes the formation of cavities and cracks at colony boundary.

Microstructure evolution and mechanical properties of Mg-Gd-Y-Zn-Zr alloy during equal channel angular pressing

The homogenized Mg-13Gd-4Y-2Zn-0.6Zr alloy was subjected to different equal channel angular pressing (ECAP) passes to investigate the effect of long period-stacking order (LPSO) phase on microstructure evolution and mechanical properties. The heterogeneous bimodal microstructure can be obtained due to the inhibition effect of intragranular 14H-LPSO phase on dislocation slip and lattice rotation at early stage. The intragranular 14H-LPSO phase was kinked and broken, which facilitate the transformation from LAGBs to HAGBs and subdivision of the deformed grains. Furthermore, the interdendritic 14H-LPSO phase was crushed and broken with further ECAP passes, which contribute to the dynamic recrystallization (DRX) process at grain boundaries via particle-stimulated nucleation (PSN) mechanism. The microstructure after 3p-ECAP demonstrates finer randomly oriented dynamic recrystallization (DRX) grains, broken 14H-LPSO phase at grain boundaries and precipitated intragranular lamellar 14H-LPSO phase. In addition, the alloy after 3p-ECAP exhibits the ultimate tensile strength of 361 MPa, tensile yield strength of 197 MPa and fracture elongation of 9.3%. The elevated temperature ultimate tensile strength after 3p-ECAP exceeds 300 MPa at test temperature of 300 ℃ and strain rate of 0.001/0.003 s−1, which can be ascribed to the broken 14H-LPSO phase at grain boundaries and precipitated lamellar 14H-LPSO phase within DRX grains.

Mechanical properties and thermal stability of carbide dispersion strengthened CLF-1 steel

One material with the same chemical composition as CLF-1 steel (defined as “base”) and three carbide dispersion strengthened CLF-1 steels with Al4C3, Ti3SiC2 and Cr2AlC additions were fabricated (defined as “+Al4C3”, “+Ti3SiC2”, and “+Cr2AlC” steel), respectively, via mechanical alloying and hot isostatic pressing (HIP). The room temperature ultimate tensile strength (UTS) of the as-HIPed “+Al4C3” steel reaches 1400 MPa and shows effective strengthening. However, after 1250 °C annealing, the “+Ti3SiC2” and “+Cr2AlC” steels show higher hardness and tensile strength than that of the “+Al4C3” steel. Transmission electron microscopy (TEM) results reveal that nano-particles in the “+Ti3SiC2” and “+Cr2AlC” steels are almost homogenously distributed inside the grains, while for the “+Al4C3” steel, distribution of nano-particles is quite scattered and shows weak connectivity to the matrix. After 1350 °C annealing, all the nano-particles in the three carbide dispersion strengthened steels are almost dissolved into the matrix.

Microstructure and properties of as-cast Cu-Cr-Zr alloys with lanthanum addition

Cu-0.45Cr-0.2Zr-xLa (x = 0–0.48) alloys were prepared by vacuum casting. The effects of La addition and orientation on the microstructure and properties of the as-cast alloy were investigated by an optical microscope, a scanning electron microscope with an energy dispersive X-ray spectrometer, a tensile testing machine and an electrical conductivity tester. The result shows that the addition of La significantly refines the columnar grainsize and decreases the secondary dendrite arm spacing. Trace addition of La improves the room temperature ultimate tensile strength, elongation and electrical conductivity mainly by purifying during melting and casting. The ultimate tensile strength, elongation and electrical conductivity significantly decrease with the increase of La content due to formation of coarse particles and oxides, which severely harm the performance of the Cu-0.45Cr-0.2Zr-xLa alloys. The Cu-0.45Cr-0.2Zr-0.13La alloy possesses a good combination of room temperature ultimate tensile strength, elongation and electrical conductivity. In addition, room temperature ultimate tensile strength and electrical conductivity along transverse direction of the ingot are higher than that along longitudinal direction, which is mainly ascribed to different distribution of grain boundary and grain orientation.

Microstructural evolution, phase constitution and mechanical properties of directionally solidified Mg-5.5Zn-xGd (x = 0.8, 2.0, and 4.0) alloys

The microstructural evolution, phase constitution and mechanical properties of directionally solidified Mg-5.5Zn-xGd (x = 0.8, 2.0, and 4.0) alloys were firstly investigated under G = 30 K/mm at a wide range of V (10 μm/s - 100 μm/s). It was confirmed that there existed α(Mg) + I(Mg3Zn6Gd) in Mg-5.5Zn-0.8Gd alloy, and α(Mg) + I(Mg3Zn6Gd) + W(Mg3Zn3Gd2) in Mg-5.5Zn-(2.0, 4.0)Gd alloys, respectively. The criterion growth rate for cellular-columnar dendrite transition (CDT) for Mg-5.5Zn-xGd alloys decreased with the increase of Gd content. The relationships between the microstructural parameters (λ1, λ2) and V for Mg-5.5Zn-xGd alloys were established using a linear regression analysis. The values of λ1 and λ2 decreased exponentially with the increase of V and the exponent values were found to be close to the theory values of 1/4 and 1/3, respectively. The tensile test showed that the room temperature ultimate tensile strength (UTS) increased and the elongation decreased with the increase of the growth rate for a certain composition of Mg-5.5Zn-xGd alloy. For a certain growth rate, UTS first increased from 0 wt % to 2.0 wt % of Gd content, and then decreased with the further increase of Gd content. The directionally solidified Mg-5.5Zn-2.0Gd experimental alloy showed the maximum ultimate tensile strength.

Al based ultra-fine eutectic with high room temperature plasticity and elevated temperature strength

Developments of aluminum alloys that can retain strength at and above 250°C present a significant challenge. In this paper we report an ultrafine scale Al–Fe–Ni eutectic alloy with less than 3.5at% transition metals that exhibits room temperature ultimate tensile strength of ~400 MPa with a tensile ductility of 6–8%. The yield stress under compression at 300°C was found to be 150 MPa. We attribute it to the refinement of the microstructure that is achieved by suction casting in copper mold. The characterization using scanning and transmission electron microscopy (SEM and TEM) reveals an unique composite structure that contains the Al–Al3Ni rod eutectic with spacing of ~90nm enveloped by a lamellar eutectic of Al–Al9FeNi (~140nm). Observation of subsurface deformation under Vickers indentation using bonded interface technique reveals the presence of extensive shear banding during deformation that is responsible for the origin of ductility. The dislocation configuration in Al–Al3Ni eutectic colony indicates accommodation of plasticity in α-Al with dislocation accumulation at the α-Al/Al3Ni interface boundaries. In contrast the dislocation activities in the intermetallic lamellae are limited and contain set of planner dislocations across the plates. We present a detailed analysis of the fracture surface to rationalize the origin of the high strength and ductility in this class of potentially promising cast alloy.

Powder metallurgy routes toward aluminum boron nitride nanotube composites, their morphologies, structures and mechanical properties

Aluminum/boron nitride nanotube (BNNT) composites with up to 5wt% (i.e., 9.7vol%) nanotube fractions were prepared via spark plasma sintering (SPS) and high-pressure torsion (HPT) methods. Various microscopy techniques, X-ray diffraction, and energy dispersive X-ray analysis confirmed the integration of the two phases into decently dense and compact composites. No other phases, like Al borides or nitrides, formed in the Al–BNNTs macrocomposites of the two series. The BNNTs were found to be preferentially located along Al grain boundaries in SPS samples (grain size was 10–20μm) creating micro-discontinuities and pores which were found to be detrimental for the sample hardness, whereas in HPT samples, the tubes were rather evenly distributed within a fine-grained Al matrix (grain size of several hundred nm). Therefore, the hardness of HPT samples was drastically increased with increasing BNNTs content in Al pellets. The value for Al–BNNT 3.0wt% sample was more than doubled (190MPa) compared to a pure Al–HPT compact (90MPa). And the room temperature ultimate tensile strength of Al–BNNTs HPT samples containing 3.0wt% BNNT (~300MPa) became ~1.5 times larger than that of a BNNT-free HPT–Al compact (~200MPa).

Microstructure Evolution and Mechanical Properties of an Al-Si-Cu-Mg-Ni Aluminium Alloy after Thermal Exposure

The microstructures and mechanical properties of an Al-Si-Cu-Mg-Ni aluminium alloy have been investigated after thermal exposure at 350 °C for time intervals up to 1000 h. Experimental results showed that, with increasing the thermal exposure time, room temperature ultimate tensile strength, elevated temperature ultimate tensile strength, and Brinell hardness firstly decreased remarkably (up to 100 h) and then decreased slightly to a certain constant value (100-1000 h). Before thermal exposure, room temperature ultimate tensile strength, elevated temperature ultimate tensile strength, elevated temperature elongation percentage, and Brinell hardness of the alloys are 203.5 MPa, 48.7 MPa, 9.2%, and 82.3, respectively. With increasing the thermal exposure time, eutectic silicon grows up steadily, and the amount of Q phase with a flower shape increases. Transmission electron microscopy analysis showed that the formation of stable θ precipitates was found in the microstructure.

Low temperature mechanical properties of as-extruded Mg–10Gd–3Y–0.5Zr magnesium alloy

Influence of multi-cycle cryogenic treatment and tensile temperature on microstructure, mechanical properties and fracture mechanism of as-extruded Mg–10Gd–3Y–0.5Zr magnesium alloy was investigated. The results show that there have no significant changes in tensile properties of the tested alloy after 10 d in liquid nitrogen immersion or 10 cycles of high-low temperature treatment at all test temperatures. The room temperature ultimate tensile strength increases from 398 MPa to 417 MPa after 20 cycles of high-low temperature treatments. Compared with the room temperature, the tested alloys exhibit higher tensile properties at low temperatures. At −196 °C, the yield strength and ultimate tensile strength of the as-extruded-T5 Mg–10Gd–3Y–0.5Zr alloy are 349 MPa and 506 MPa, respectively, increasing by about 18% and 27%, respectively. The transgranular cleavage fracture mechanism is observed at room temperature, while at low temperatures both ductile fracture and cleavage fracture behaviors coexist.

Effect of heat treatment on microstructures and tensile properties of as-forged Ti-45Al-5Nb-0.3Y alloy

In this article, the canned forging pancake was successfully gained, and the effects of heat treatment on microstructures and mechanical properties of as-forged Ti-45Al-5Nb-0.3Y have been studied. Three different microstructures, duplex (DP), nearly lamellar (NL) and fully lamellar (FL), have been obtained through different heat treatments, respectively. And the microstructure evolution was also analyzed. The room temperature tensile properties of the as-forged alloy depend on heat treatment. After treated at the condition of 1320 °C for 30 min, the room temperature elongation of the alloy increased obviously. And the as-forged sample treated at 1370 °C for 15 min, with FL structure, exhibited higher room temperature ultimate tensile strength (715.1 MPa) than the samples treated by other conditions.