Room Temperature Tensile Fracture Research Articles

A novel NbTaV0.5Hf0.1 complex concentrated alloy with superior room-temperature tensile plasticity and elevated-temperature strength

Refractory complex concentrated alloys (RCCAs) encounter difficulties in balancing room-temperature ductility and high-temperature strength, which restricts their applications. Here, a novel NbTaV0.5Hf0.1 RCCA was prepared through vacuum arc melting for the first time. The as-cast alloy exhibited a stable body-centered cubic phase structure with a small amount of micro-scale dispersed Hf-rich oxides. As a result, the designed alloy exhibits a room-temperature tensile fracture strain of 14.9 %, and superior compressive yield strength values under elevated temperatures (472 MPa under 1200 ℃, 358 MPa under 1400 ℃, respectively). A synergy between room-temperature tensile ductility and exceptional high-temperature strength was achieved in RCCAs.

Tensile behavior of the designed SiCf/Ti2AlNb/Ti17 composites

SiCf/Ti2AlNb-reinforced Ti17 (SiCf/Ti2AlNb/Ti17) composites were fabricated through hot isostatic pressing. The designed SiCf/Ti2AlNb/Ti17 composites exhibited excellent tensile properties, with tensile strengths of 1657 MPa at room temperature and 1830 MPa at 450 °C. The microstructure, fracture morphology, and longitudinal section of the composites were characterized by X-ray diffraction, scanning electron microscopy, and electron backscatter diffraction techniques. The fracture process of SiCf/Ti2AlNb/Ti17 composites during room-temperature tensile tests was as follows: the SiCf/Ti2AlNb reaction layer first fractured, the crack extended into the Ti2AlNb matrix, the Ti2AlNb matrix crack extended to the adjacent reaction layer and promoted fiber fracture, the crack extended to the Ti2AlNb/Ti17 interface, ultimately the Ti17 capsule fractured. The fracture process of SiCf/Ti2AlNb/Ti17 composites during 450 °C tensile tests was as follows: the SiCf/Ti2AlNb reaction layer first fractured, multiple fiber fractures occurred, and the crack in the reaction layer entered the Ti2AlNb matrix, the crack extended to the Ti2AlNb/Ti17 interface, eventually the Ti17 capsule fractured. The room-temperature tensile fracture was fitted to the LLS model, while the tensile fracture at 450 °C was fitted to the GLS model. The different fracture processes indicated that the SiCf/Ti2AlNb/Ti17 composites were suitable for exploiting fiber strength at 450 °C and therefore exhibited excellent tensile strength.

The Room Temperature Fracture Behaviors of GNPs/TA15 Composites by Pre-Sintering and Hot Extrusion.

Graphene nanoplates (GNPs)/TA15 composites were fabricated by pre-sintering and hot extrusion. During a room temperature tensile test, the dislocation was generated in grains. With increasing strain, the dislocation piled up along the interface between GNPs and Ti matrix, leading to stress concentration and microcracks. Then, the microcracks extended to GNPs or along the interface. The GNPs cracked under the shear force and the GNPs pulled out along with the crack propagation along the interface. This work provides a new sight in the room temperature tensile fracture behaviors.

Study on Tensile Fracture Behavior of New Type High Temperature Titanium Alloy Ti-Al-Nb at Room Temperature

In this paper, in order to explore the development of a titanium-based superalloy with a working temperature of 700°C to 750°C and good ductility at room temperature, using Ti+Al+Ti2AlNb ternary powder as the raw material, the temperature is 1200°C to 1300°C, 30MPa, 1.5h Directly mixed and sintered under hot pressing conditions, a new type of titanium-based superalloy (TiAl+Ti2AlNb) samples were prepared. The fracture morphology of hot-pressed sintered samples and tensile samples used scanning electron microscope (Scanning electron microscope, referred to as SEM) and Electron backscattered diffraction (EBSD) for observation. Discuss the room temperature tensile fracture behavior of a new type of high temperature titanium alloy Ti-Al-Nb, and lay a technical foundation for the development of a new type of high temperature titanium-based alloy with low brittleness at room temperature.

5083 aluminum alloy sheet with excellent mechanical properties fabricated by constrained ring groove pressing based on a cyclic stress state

A new process of repeated compression and deformation by warm and circular waves based on a cyclic stress state is proposed. This process prepares 5083 aluminum alloy plates with greatly improved mechanical properties. Results show that the overall thickness of the sheet is relatively uniform after ring wave deformation. As the flattening temperature increases, the uniformity of the sheet thickness improves. First, the grain refinement effect is the best after four passes of deformation when the flattening temperature is 200 °C, and the average grain size is refined from 24 μm to 8.0 μm. As such, the hardness of the obtained sheet is the largest, and the Vickers hardness increases from 82.3 HV to 101.6 HV. Second, the mechanical properties of the sheet after three passes of deformation are better when the flattening temperature is 250 °C. The tensile strength and the fracture elongation greatly improve. The tensile strength is 295 MPa, which is 10.7 % stronger than the original sheet. Fracture elongation is 28.76 %, which corresponds to a 56.3 % increase compared with that of the original sheet. Third, when the flattening temperature is 300 °C, the comprehensive mechanical properties of the sheet after three passes of deformation are the best. The tensile strength of the sheet is 289.6 MPa, which is 8.6 % higher than that of the original sheet, and the maximum elongation at break is 32.2 %, which is 75.0 % higher than that of the original sheet. The SEM morphology of the room-temperature tensile fracture of the sheet with different deformation conditions shows that the number of micropores and dimples in the room-temperature tensile fracture, the maximum size, and the number of white tear edges increase as the flattening temperature increases. Consequently, sheet toughness and plasticity improve.

Effect of heat treatment on microstructure and mechanical properties of Mg-4Y-1.6Nd-1Sm-0.5Zr alloy

Microstructure and mechanical properties of Mg-4Y-1.6Nd-1Sm-0.5Zr alloy during heat treatments were investigated, while the room-temperature tensile fractographs were observed and analyzed. The results show that the eutectic phases almost dissolve into the matrix after being solutionized at 525 °C for 8 h. The ultimate tensile strength, yield strength and elongation reach 300 MPa, 219 MPa, 6.5% respectively after being under-aged at 200 °C for 16 h. The ultimate tensile strength and yield strength of the alloy decrease gradually, while the elongation increases gradually with increasing the test temperatures. The room-temperature tensile fracture modes of the as-cast alloy, solutionized alloy, aged alloy are mixed fracture of transgranular and intergranular, transgranular cleavage fracture, transgranular fracture, respectively.

Room temperature tensile fracture characteristics of the oriented TiB whisker reinforced TA15 matrix composites fabricated by pre-sintering and canned extrusion

In situ oriented TiB whisker reinforced TA15 matrix composites (TiBw/TA15) exhibited an improvement of tensile properties. The strain hardening after yield point was almost counteracted by the reduced effective cross-sectional area caused by the whisker fracture, thus resulting in a large yield strength ratio.

Tensile deformation and fracture of Ti–5Al–5V–5Mo–3Cr–1.5Zr–0.5Fe alloy at room temperature

A combination of transmission electron microscopy, scanning electron microscopy and x-ray diffractometer is used to analyse the deformation mechanism and the fracture behavior of bi-model structure Ti–5Al–5V–5Mo–3Cr–1.5Zr–0.5Fe alloy during uniaxial tensile test. In the uniform deformation region, the strain of the primary α particles is dominated by the planar slipping and the dislocation tangling, and the deformation of the β matrix is accompanied by the dislocation tangling. In the necking region, the additional deformation twinning is found in the primary α particle, and the β phase is still strained by the dislocation tangling. The local shearing occurs in the necking region and results in the micro-twinning dominated deformation in secondary α precipitation and the 〈110〉β fiber texture. The room temperature tensile fracture of Ti-55531 alloy is extremely sensitive to the formation of the voids, and the critical dimension of the crack is the diameter of the primary α particles.

Influence of forging process on microstructure and mechanical properties of large section Ti–6.5Al–1Mo–1V–2Zr alloy bars

The mechanical properties, microstructure and tensile fracture of Ti–6.5Al–1Mo–1V–2Zr large section bars produced by three diffrent forging processes were investigated. The results show that when billet forging and finish forging were conducted by means of fullering at high and low temperature of β-region, respectively; the microstructure of forged bar is coarse Widmanstaten structure; the mechanical properties, especially the reduction of cross-sectional area, are poor, and the room temperature tensile fracture presents a brittle feature. While billet forging was carried out by upset-fullering at high temperature of the β-region, and finish forging was proceeded through fullering at (α+β)-region, the microstructure of forged bar was a duplex structure, the bar has better comprehensive mechanical properties, and the room temperature tensile fracture reveals a ductile feature. In order to obtain qualified Ti–6.5Al–1Mo–1V–2Zr alloy bar, it is the key that as-cast microstructure should be completely broken during billet forging, and the forging temperature and deformation are also well controlled upon finishing forging.

Effect of 950 °C Thermal Exposure on Microstructures and Properties of Ni-Based K403 Alloys

Abstract Thermal exposure experiments of Ni-based cast superalloy K403 at 950 °C for 5, 50 and 100 h were conducted. The effect of thermal exposure on the microstructures and room-temperature mechanical properties of the superalloys K403 was studied. The results show that M6C carbides segregate from intra-grains and grain boundaries, and γ′ phases aggregate and grow up with blunted corners. With increasing of thermal exposure time, on the one hand, γ′ phases of spherical or nearly spherical shapes are formed from blunted corners and parts of the γ′ phase tend to coarsen due to the connection-oriented effect. On the other hand, the offset yielding stress and the tensile strength decrease, while the plasticity improves obviously, resulting from the aggregation and coarsening of the γ′ strengthening phase. The room-temperature tensile fracture surface is characterized by the dendritic structure fracture for K403 alloys before and after the thermal exposure. Whereas the intercrystalline fracture feature, and the shallow and small dimples appear on the tensile section of the thermal-exposed alloys. And the amount of dimples increases as the exposure time increases.

The mechanical behaviour of an ultrafine grained Ti–47Al–2Cr (at%) alloy in tension and compression and at different temperatures

A bulk ultrafine grained (UFG) Ti–47Al–2Cr (at%) alloy has been produced using a powder metallurgy process that combines high energy mechanical milling (HEMM) of a mixture of Ti, Al and Cr powders to produce a Ti/Al/Cr composite powder and hot isostatic pressing (HIP) of the composite powder compact. The purpose of the present study is to determine the mechanical behaviour of the alloy in tension and compression at room temperature (RT) and elevated temperatures, and also to compare the compression behaviour of the material with its tensile behaviour. It has been found that due to the residual pores, lack of full level interparticle bonding and high oxygen content (0.87 wt%) in the consolidated samples, the UFG TiAl based alloy has a very low room temperature tensile fracture strength of ∼100 MPa and shows no tensile ductility. However these microstructural defects and high oxygen content have much less significant effect on the room temperature compressive mechanical properties, and the alloy shows a high compressive yield strength of ∼1410 MPa, and some ductility (plastic strain to fracture ∼4%). At elevated temperatures of 800 °C and above, the alloy shows high tensile and compressive ductility as demonstrated by 75% tensile elongation to fracture and no cracking in upset forging with a height reduction of 50% at 900 °C. The yield strength of the alloy at 900 °C is 55 MPa in tension and ∼33 MPa in compression, both of which are lower than those of coarse grained TiAl based alloys with similar compositions at 900 °C. This is due to a higher creep rate of the UFG alloy caused by the small grains. The good formability of the UFG TiAl based alloy as reflected by the lower critical temperature above which the alloy becomes highly formable indicates that the material can be used as a suitable precursor for secondary thermomechanical processing and super-plastic forming.

Room temperature tensile fracture characteristics of in situ TiBw/Ti6Al4V composites with a quasi-continuous network architecture

In situ TiB-whisker-reinforced Ti6Al4V matrix composites with a quasi-continuous network reinforcement distribution exhibited an improved combination of room temperature tensile properties compared to the composites with a uniform reinforcement distribution. The unique microstructure consisting of a whisker-rich boundary region and a whisker-lean matrix region leads to unique fracture characteristics . Under tensile stress, the main crack follows the TiBw-rich region, which imparts the superior strengthening effect of TiBw. The relatively large TiBw-lean region contributes positively to the elongation to failure of the composites.

Influence of Isothermal Deformation Conditions on The Mechanical Properties of 22MnB5 HPF Steel

AbstractIn the present study, the aluminized 22MnB5 Hot Press Forming (HPF) steel was deformed isothermally in the temperature range of 600–800 °C. The specimens were deformed with 0%, 10% and 30% engineering strain at a strain rate of 0.5/s. Mechanical stabilization of austenite during phase transformation was observed. The influence of strain rate was also studied. It was found that the martensite transformation was affected by the combined effect of mechanical stabilization and dynamic recovery. The influence of high temperature deformation on the final microstructure, microhardness and mechanical properties were studied. Deformation applied below 750 °C resulted in a significant decrease of the strength and the hardness. The ferrite fraction and morphology had a clear effect on the room temperature tensile fracture morphology.

The effects of interfaces on the mechanical properties of Ni–Al–Fe intermetallics

The casting Ni–25Al– xFe alloys had dendritic microstructures, and the two major phases existing in these alloys were B2 (ordered b.c.c.) phase in dendrites and f.c.c. phase in interdendrites. The B2 phase exhibited a higher hardness and was more brittle by comparison with the f.c.c. phase in interdendrites, and the two phases showed different plastic deformation results during tensile test. Cracks nucleated at the interfaces between these two phases during tensile stress, then propagated and the specimen failed. The room temperature tensile fracture modes were a mixture of dimple and cleavage. Changing the testing temperature or the mole fraction of elements in the alloys changed the fracture mode and mechanical properties.

Microstructure investigation in B2-phased Ni-25Al-40Fe intermetallic compound

The casting Ni–25Al–xFe alloys had dendritic microstructures, and the two major phases existing in these alloys were B2 (ordered b.c.c.) phase in dendrites and f.c.c. phase in interdendrites. The B2 phase exhibited a higher hardness and was more brittle by comparison with the f.c.c. phase in interdendrites, and the two phases showed different plastic deformation results during tensile test. Cracks nucleated at the interfaces between these two phases during tensile stress, then propagated and the specimen failed. The room temperature tensile fracture modes were a mixture of dimple and cleavage. Changing the testing temperature or the mole fraction of elements in the alloys changed the fracture mode and mechanical properties.

The role of active elements in Fe-Cr-Al alloys for heating element applications

The role of active elements (zirconium, cerium and yttrium) in grain growth and its subsequent effect on room-temperature tensile fracture behaviour of Fe-Cr-Al alloys has been investigated. The alloys containing active elements exhibited improved resistance to grain growth. Yttrium-containing alloy retained higher room-temperature tensile ductility even after heating at higher temperatures because of its superior resistance to grain coarsening. All the alloys, with and without active elements, exhibited a sudden drop in room-temperature tensile ductility, with concommitant change in fracture mode from dimple rupture to cleavage, in a narrow band of 39–44µm grain size. The ductile-brittle transition temperatures (DBTT) of these alloys were found to be 150°C and 215°C for grain sizes 25µm and 100µm respectively. The accelerated life test showed that the alloys containing active elements exhibited longer lives.

Failure Modes of a Unidirectional Ultra‐High‐Modulus Carbon‐Fiber Carbon‐Matrix Composite

The objective of this study was to observe the effects of various microstructural features on the in situ, room‐temperature tensile fracture behavior of an ultra‐high‐modulus, unidirectional carbon/carbon (C/C) composite as a function of processing heat‐treatment temperature (HTT) over the range of 1100° to 2750°C. An in situ SEM flexural stage was used to observe the interactions between the advancing crack tip and the microstructural features in the frontal process zone. Following the lowest HTT of 1100°C, failure is dominated by the well‐bonded brittle matrix; a tortuous crack path in the E130 fibers appears to contribute to a relatively high utilization of fiber strength in spite of this brittle‐matrix failure. Approximate calculations of the interfacial shear stress that might be generated by matrix shrinkage during pyrolysis of the polymer to carbon were compared to approximations of crack‐tip interfacial shear stresses (IFSS) using the Cook‐Gordon approach. The results suggest that the strong bonding in the 1100°C HTT composite cannot be accounted for by friction alone, and, therefore, chemical bonding or some type of fiber‐matrix mechanical interlocking must be involved. Higher HTTs lead to progressive weakening of the fiber‐matrix interface, and, with heat treatment to 2150°C, multiple matrix cracking (MMC) is observed. Using the crack‐spacing model of Aveston, Cooper, and Kelly (ACK), an IFSS of 1 MPa is estimated for the MMC case. Attempts to calculate the matrix failure strain using the ACK formulation led to a large overprediction of the failure strain, although a number of the parameters used in the calculation are known only very approximately. Heat treatments to 2400° and 2750°C led to longitudinal intramatrix cohesive failure; at 2750°C, this damage is extensive and results in composites with strength utilizations approaching those of dry fiber bundles.

Properties of Microlaminated Intermetallic-Refractory Metal Composites

AbstractMicrolaminated composites of Nb3Al-Nb and Cr2Nb-Nb(Cr) were synthesized by high rate magnetron sputtering. Both composites were stable at elevated temperatures. A Cr2Nb-Nb(Cr) composite with 2 µm metal and intermetallic layers had room temperature tensile fracture strength over 725 MPa and a fracture toughness of about 20 MPa√m. Composites with 2 µm and 6 µm thick refractory metal and intermetallic laminations were compared and it was found that layer thickness did not affect fracture toughness. Microlaminates with the thicker 6 µm laminations had lower fracture strength, however. Good fracture strength and high fracture toughness indicated that microlaminated high temperature composites synthesized by vapor phase deposition exhibit the properties predicted by ductile toughening models.