High-temperature Compressive Properties Research Articles

In situ tailoring of precipitation behavior and improving mechanical properties of (Ti2AlC+Y2O3) reinforced TiAl alloy produced by directed energy deposition

A (Ti2AlC + Y2O3) synergistically reinforced Ti–48Al–2Cr–2Nb alloy was prepared by directed energy deposition with in situ tailoring of precipitate formation by induction preheating and thermal cycle. The influence of C and Y2O3 coaddition on the microstructure and high-temperature compressive properties was systematically investigated. The results indicated that Ti2AlC was formed by adding elemental C, and the Ti2AlC phase was mainly distributed in two forms: long rod-shaped Ti2AlC with a micron scale that distributed uniformly in the matrix, and lenticular Ti2AlC particles with nanometer size that distributed along the (α2/γ) lamellar interface. The Y2O3 particles were randomly distributed in the matrix. Columnar grains in vertical cross section along the building direction were completely eliminated by adding C and Y2O3. The high temperature compressive strength increased from 597 MPa to 758 MPa at 850 °C by adding C and Y2O3. Finally, the precipitation mechanism of nano-Ti2AlC was discussed in detail. This work provided a valuable reference for the preparation of high-performance TiAl alloys by in situ tailoring of the precipitates during the DED process.

Effect of TiB2 Addition on the Microstructure and Mechanical Properties of Laser-Directed Energy Deposition TiAl Alloy

The microstructure characteristics of TiAl alloy prepared by laser-directed energy deposition (L-DED) are coarse columnar grains parallel to the building direction, which results in serious mechanical properties and anisotropy and limits its application. In the present study, TiB2 can be used as an effective grain refiner due to the extremely high Q value (growth inhibition factor; the larger the Q value of an alloying element, the stronger its grain refinement effect.) of B. With TiB2 addition, TiAl alloys prepared by laser-directed energy deposition with the microstructure of full equiaxed grains were obtained, and the grain size was significantly reduced by about 30% with 0.45 wt.% TiB2. This value has been further increased to 45% when adding 0.9 wt.% TiB2. Moreover, the γm phase was nearly eliminated and the width of (α2 + γ) lamellar was significantly decreased, which has positive effects on mechanical properties. Meanwhile, TiB2 precipitates uniformly distribute in the matrix, as a reinforced particle to increase the hardness and compressive strength of the alloys. The microhardness of the TiAl alloy increased with the increasing content of TiB2. The addition of TiB2 improved the room and high-temperature compressive properties of TiAl alloy while slightly increasing its ductility. These findings have important guiding significance for expanding the application of TiAl alloys.

Microstructure, Compressive Properties and Oxidation Behaviors of the Nb-Si-Ti-Cr-Al-Ta-Hf Alloy with Minor Holmium Addition

In the present research, the Nb-Si-Ti-Cr-Al-Ta-Hf alloys with different Ho addition were prepared. Their microstructure, compressive properties and oxidation behaviors were investigated preliminarily. The results exhibit that the Nb-Si-Ti-Cr-Al-Ta-Hf alloy has coarse microstructure which is mainly composed of Nb solid solution, Nb5Si3 and Ti5Si3 phases. The minor Ho addition could refine the microstructure and suppress the precipitation of Ti5Si3 phase. Moreover, the Ho addition also leads to the formation of Ho2Hf2O7, which prefers to precipitate along the Nbss/Nb5Si3 phase interface. Compared with the Nb-Si-Ti-Cr-Al-Ta-Hf alloy, the minor Ho addition improves the room-temperature and high-temperature compressive properties of the alloy. Its room-temperature compressive strength and ductility obtain the maximum value of 1825 MPa and 16.5% when the Ho content is 0.1 at.%. Moreover, its best compressive strength at 873 K, 1273 K and 1473 K is 1495 MPa, 765 MPa and 380 MPa, respectively, when the Ho addition is 0.1 at.%. The oxidation behavior of the Nb-Si-Ti-Cr-Al-Ta-Hf alloy is diversified with the Ho addition. The oxidation rate of the alloy with 0.1 at.% Ho addition is the lowest while the alloy with 0.2 at.% Ho addition is the highest. Therefore, the 0.1 at.% Ho would be the appropriate content for the Nb-Si-Ti-Cr-Al-Ta-Hf alloy.

In-situ TiC/Ti composites based on Ti2AlC–Ti system: Reaction process, microstructure, and mechanical properties

Based on the improvement of the phase transition temperature of Ti by Al element and the excellent strengthening effect of TiC particles, this paper selects Ti2AlC as the precursor, striving to improve the high-temperature performance of the Ti matrix. The composites with 1–10 vol% Ti2AlC addition were fabricated by hot-pressing sintering. And a detailed study was conducted on the reaction process, microstructure, room and high temperature compression properties of the composites. The experimental results show that the separation of Al elements at the A-position occurs at around 700 °C in Ti2AlC, and the Al element is homogenized in the matrix during the subsequent sintering process. Micron sized TiC particles are mainly distributed at the Ti grain boundaries, while the content of sub-micron sized TiC particles entering the crystal increases with the increasing Ti2AlC addition. The interface mismatch between TiC and Ti is small, and the bonding is well. These microstructures enable composite materials to exhibit excellent mechanical properties, with 10 vol% Ti2AlC/Ti composite having a yield strength of 1858 MPa and an ultimate strength of 2200 MPa at room temperature, and maintaining a yield strength of 602 MPa and an ultimate strength of 1264 MPa at 500 °C.

The flow behavior and constitutive equation of (Al3Ti+Al2O3)/2024Al composites during hot compression

In this study, Al3Ti and nano-Al2O3 co-reinforced aluminum matrix composites were prepared in situ autogenously using TiO2 and Al alloys as raw materials. The high-temperature compression properties of the composites were tested at temperatures ranging from 300 to 500 °C and strain rates ranging from 0.0014 s−1 to 0.42 s−1. Excellent high-temperature properties were demonstrated due to the presence of a large amount of Al3Ti and nano-Al2O3 high-temperature phases in the composites. The peak compressive stress of (Al3Ti+Al2O3)/2024Al composites gradually decreases with increasing temperature and increases with increasing strain rate. The study also calculated the deformation activation energy of the composites and the intrinsic structure model during hot compression. This is a guideline for obtaining the material thermal processing conditions of new composites with excellent high-temperature properties.

Revealing the ultra-high high-temperature compressive mechanical properties and deformation mechanism of a heterostructured AlNp/Al nanocomposite

Heterostructured materials have attracted increasing attention owing to their superior mechanical properties. In this work, the high-temperature mechanical property and deformation mechanism of a heterostructured AlNp/Al composite were revealed by isothermal compression tests. The results showed that the superior compressive strength of the AlNp/Al composite could be maintained at both room temperature and high temperature of 300–500 °C during the whole deformation process. The strong pinning effect of the dispersive AlN nanoparticle (AlNp) on the matrix grains could prevent grain boundary softening and grain growth, as well as the special layered heterogeneous structure and network structure could avoid high temperature softening. The hot deformation mechanism of the AlNp/Al composite could be affected by the strain rate and deformation temperature. It was confirmed that continuous dynamic recrystallization (CDRX) dominated the whole deformation process when deformed at low strain rates (0.0001–0.01 s−1) and high temperatures (400–500 °C); while dynamic recovery (DRV) was the main mechanism at high strain rate (0.1–1 s−1) and low temperature (300–350 °C) Furthermore, the strain rate sensitivity exponent (m) was used to assess the relationship between peak stress and deformation temperature and strain rate, which could predict the instability region of the composite. It shows that the simultaneous action of high temperatures and high strain rates should be avoided during hot deformation. This work shed light on the microstructure design of the high-strength heat-resistant aluminum matrix composite.

A novel coherent particles-reinforced FCC-based high-entropy superalloy with superior high-temperature compressive properties

A novel κʹ-strengthened FCC-based Al0.5CoFeNiC0.1 high entropy superalloy (HESA) with minor B2 phase was prepared by arc melting. The FCC/κʹ dual-phase microstructure with thermal stability is similar to γ/γʹ microstructure of Ni-based superalloys. Surprisedly, the large volume fraction (nearly 50%), high density and nano-scale coherent κʹ particles with uniform distribution are easily accessible only by direct solidification, which gives rise to superior compressive yield strengths at both room and elevated temperatures, reaching 1130 MPa at 25 °C and 830 MPa at 700 °C, respectively. The sustained high-temperature yield strength is contributed to both the antiphase boundaries (APBs) and stacking faults (SFs) shearing κʹ particles. Further, optics and electron microscopy analyses revealed the changes (transition point about at 0.6 Tm, where Tm is melting temperature) of the dominant deformation and failure mechanisms, dependent on the temperature. The dominant deformation mode is planar slip and SFs at relatively low temperatures, while the cross slip and dislocation dissociation above 800 °C (0.6 Tm), coupled with the diffusion-controlled recovery mechanisms. The failure mechanism shows failure mode from shearing fracture to thermal softening. Our κʹ-strengthened FCC-based superalloy provides a route for elevated-temperature applications.

Effect of Grain Refinement on the Comprehensive Mechanical Performance of W-Cu Composites.

W-Cu composites are commonly subjected to coupled multiple fields in service, which imposes high requirements on their overall performance. In this study, the ultrafine-grained W-Cu composite was fabricated using the combination of electroless plating and spark plasma sintering. The wear resistance and high-temperature compressive properties of the ultrafine-grained W-Cu composite were investigated and compared with those of the commercial coarse-grained counterpart. Moreover, the underlying strengthening and wear mechanisms were also discussed. Here we show that the ultrafine-grained W-Cu composite exhibits superior integrated mechanical performance, making it a potential alternative to commercial W-Cu composites.

Research on High-Temperature Compressive Properties of Ti–10V–1Fe–3Al Alloy

To investigate the thermal deformation behavior of Ti–10V–2Cr–3Al titanium alloy, the hot compression experiments were carried out via a strain rate of 0.1–0.001 s−1 and deformation temperature of 730~880 °C. The results showed that the rheological stress decreases when the deformation temperature increases or strain rate decreases. Due to the deformation conditions, some flow curves exhibited significant discontinuous yielding and flow softening. Flow softening in the α+β phase region was dominated by dynamic recrystallization (DRX), while in the β phase region, it was centered on dynamic recovery (DRV). A high-temperature constitutive equation, with good predictive power, was established.

High-Temperature Compressive Response of SiCp/6092Al Composites under a Wide Range of Strain Rates.

The high-temperature dynamic compressive properties of a 30 vol.% SiCp/6092Al composite, fabricated using powder metallurgy, were experimentally investigated using the split Hopkinson pressure bar system with an electric furnace. Three different ambient temperatures, namely, room temperature, 200 °C, and 350 °C, were adopted, and the dynamic tests of the composite specimens were conducted at strain rates ranging from 1500 to 4500 s−1. The experimental results showed that the flow stress of the composite was generally insensitive to strain rates at room temperature. However, the composite started exhibiting different strain-rate-dependent behaviors as the temperature increased, and the flow stress nonlinearly varied with increasing temperature. In addition, the microscopic images of the specimens showed that the microscopic failure mechanisms of the composite were greatly influenced by the ambient temperature and strain rate. Specifically, the percentage of failed particles decreased with rising temperature and the dominating failure mode of particles changed significantly as the strain rate increased.

Microstructure and high temperature mechanical properties of advanced W–3Re alloy reinforced with HfC particles

W–3Re alloys reinforced with various HfC particles contents (0 wt%, 0.5 wt%, 1 wt%, 5 wt%, 10 wt%) were fabricated using spark plasma sintering (SPS) at 2050 °C for 10 min. Microstructure, Vickers hardness and high temperature compression properties of the sintered W-3Re-xHfC alloys were investigated. Spherical HfC nanoparticles and micron scale clusters are distributed at the grain boundaries of the W–Re matrix. These nanoscale HfC particles pin dislocations and grains boundary as well as refine grain, thus enhancing the strength of composites. Furthermore, the HfC-W interfaces are well bonded semi-coherently without apparent interfacial gaps. The high temperature strength and micro-hardness of sintered composites are significantly increased with an increase of HfC contents. The micro-hardness of W–3Re alloy was 659.4 HV when 10 wt % HfC was added, which is enhanced up to 92.5 % compared with matrix. Its compressive strength is 850 MPa, increased by ~286 % compared with that of W–Re matrix. Quantitative analysis indicates that the main strength mechanisms are grain refinement, Orowan strengthening and interfacial thermal mismatch strengthening, which are influenced significantly by the HfC contents. This study provides new insights into composites performance optimization, reinforcement designs and strengthening mechanisms of particles reinforced W matrix alloys.

Microstructures and mechanical properties of Ti–44Al–5Nb–3Cr–1.5Zr–xMo–yB alloys

Abstract

Tailoring the microstructure and properties of tungsten-copper composites by minor addition of SiC particles for nuclear fusion reactor application

In this work, minor addition of SiC ceramic particles were tested to tailor the microstructure and properties of infiltrated tungsten-copper (W–Cu) composites. The resultant microstructure, density, electrical conductivity, compressive behavior and arc resistant property of the WCu-x wt%SiC (x = 0.5, 1, 2, 3) composites were studied in comparison. The phase constituents of bcc-W, fcc-Cu and hcp-SiC were confirmed by X-ray and electron diffraction techniques. It is also revealed that gradual sintering growth of W particles occurred with the increasing content of SiC under the same processing and sintering parameters. Besides, with the increase of the mixed SiC, the density and electrical conductivity showed a steady decreasing trend due to the retarded rearrangement of W during sintering and the inherently low conductivity of SiC. Specifically, the composite of WCu–2%SiC exhibited the highest room-temperature strength of 1323 MPa and the highest particle-particle contiguity value of 0.373. Moreover, it showed excellent high-temperature arc resistance and compressive properties. Electron backscattering diffraction (EBSD) analysis further validated that the origin of its high damage tolerance can be attributed to its hierarchical microstructure both in grain size and misorientation.

High temperature compressive properties and microstructure of WC-Ni3Al cermets prepared by spark plasma sintering

WC-Ni3Al cermets were prepared using powder metallurgy methods and spark plasma sintering. The high temperature compressive properties of WC-Ni3Al cemented carbide with different Ni3Al content were investigated at 850 °C. The existence of antiphase boundary in the Ni3Al binder phase was found to improves the stress state in the WC matrix. Ni3Al can coordinate the deformation of WC more effectively, thus obtaining increased plasticity and strength. In addition, the dislocation movement and deformation mechanisms of the WC grains during high temperature compression were also studied. The results show that the (011‾0) plane in WC grain is the habit plane for slip at high temperature.

Effect of La/Nd ratio on microstructure and mechanical properties of as-cast AZ91-xLa/Nd alloy

The effect of La/Nd ratio on microstructure and mechanical properties of as-cast AZ91D alloys were investigated. The alloys were produced by casting the molten metal into a preheated steel mould. Microstructures were investigated by XRD and SEM (equipped with EDS). The hardness measurement was carried out by Brinell hardness (HB) digital display tester. Compression tests were conducted at both room and high temperatures (20 °C and 150 °C). Microstructural characterizations reveal that the area fraction of the β-Mg17Al12 phase changed with the variation of La/Nd ratio. The area fraction of the β-Mg17Al12 phase decrease significantly and then increased slightly with the increase of La/Nd ratio. Besides, the results show that the addition of La and Nd contributed to the formation of needle-like phase Al11RE3. Meanwhile, the Brinell hardness and high-temperature compression properties of this alloy reach the maximum values (67 HB and 330 MPa, respectively) when the La/Nd ratio is 2/3. In this alloy, the amount of Al11RE3 phase is 51/TA and the average length is 69.55 μm. Moreover, a generation model of Al11RE3 is established and the growth mechanism of Al11RE3 is analyzed. This work thus has proved that La/Nd ratio has a great effect on the microstructure and mechanical properties of AZ91.

High-temperature compressive properties and tribological behaviour of Mo2NiB2–Ni cermets

The present work investigated the high-temperature compressive strength and tribological behaviours of Mo 2 NiB 2 –Ni cermets from 25 to 900 °C. Mo 2 NiB 2 –Ni cermets with four different Ni additions were first fabricated successfully and then tested. The results show that cermets with Ni/B 1.1 have the best compressive strength of 531.8 MPa at 900 °C and superior strength retention at high temperature. With the best high-temperature compressive strength, Mo 2 NiB 2 –Ni cermets with Ni/B 1.1 are used as pins with Si 3 N 4 disks in a tribological test. The wear rate of Mo 2 NiB 2 –Ni cermets gradually increases as the temperature increases from 25 to 900 °C, while the friction coefficient shows the opposite trend. Within the entire testing temperature range, the friction coefficient decreases, and the minimum friction coefficient is obtained at 900 °C. The decline of the friction coefficient is attributed to the self-lubricating oxidation tribolayer covering the worn surface. Moreover, the dominant wear mechanism changes from abrasive wear to oxidation wear as the temperature exceeds 600 °C.

Microstructure and high temperature compressive properties of Nb-based alloys fabricated by plasma arc-induction hybrid melting

A new melting system called plasma arc-induction hybrid melting technology was designed in this work to fabricate Nb-based alloys, which combines the advantages of plasma arc melting and levitation melting. The ternary alloy Nb-16Si-22Ti alloy ingot prepared by the new method was found to have a high level of chemical homogeneity with the difference of <0.5 at% in the concentration distribution. Three alloys C103, C109 and M532, which are the widely used alloy grades in industry, are chosen as base. Then, 16%Si and 22%Ti was added in the three base alloys and new alloys BC103, BC109 and BM532 were obtained to study the effects of Si and Ti addition on the microstructure and mechanical properties of Nb-based alloys. Among them, alloy Nb-16Si-22Ti-5Mo-2Cr-2Al-2Hf (BM532) was found to have the best high temperature compressive properties, which was used as base and W element was added as a replacer of Hf by 0, 1, 2 at% to further improve the high temperature mechanical strength of the alloy. The results indicated that alloy Nb-16Si-14Ti-5Mo-2Cr-2Al-1W has the best high temperature compressive properties, with a compressive strength of 1034 MPa at 1200 °C and 725 MPa at 1500 °C.

Cryogenic and high temperature compressive properties of Metal Foam Matrix Composites

The cryogenic (−196 °C), room (25 °C) and high (250 °C) temperature compressive crushing performances of recently developed metal foam matrix composites was investigated with respect to the position of reinforcements on foam samples. Closed-cell aluminum alloy foams were produced via powder metallurgical route from AlSi10 matrix material; while diamond shape expanded stainless steel were used as reinforcements. The deformation behavior and main mechanical properties of the unreinforced and reinforced metallic foam was found to be strongly temperature dependent under quasi-static loading. Reinforced foams exhibited much higher strength properties and energy absorption capability compared to unreinforced foams at almost the same overall weight of the samples, i.e. up to 11 times. The properties percentage reductions of the reinforced foams are significantly below the reduction of the unreinforced foam. Furthermore, it was observed that the collapse mechanisms and mechanical properties of the reinforced foams depends on reinforcement position.

Microstructural evolution and high-temperature compressive properties of an extruded Mg–Dy–Zn alloy sheet

Abstract Microstructural evolution and compressive properties of an extruded Mg-2Dy-0.5Zn (at.%) alloy sheet at 350°C were investigated. As the compressive strain increased, the volume fraction of dynamic recrystallization increased, the fine lamellar 14H long period stacking ordered phase precipitated in the dynamic recrystallization grain, and the Mg12ZnDy phase with an 18R long period stacking ordered structure gradually bent. These secondary phases not only acted as nucleation sites to promote dynamic recrystallization but also restrained grain growth by inhibiting dislocation movement and grain boundary sliding. The compressive yield strength, ultimate compressive strength, and compressive strain of the alloy sheet were 161 MPa, 212 MPa, and 12.4% at 350°C, respectively. The high compressive strengths were mainly attributed to grain refinement, kink band strengthening of the 18R long period stacking ordered phase and precipitation strengthening of the fine lamellar 14H long period stacking ordered phase in the dynamic recrystallization grain.

High temperature compression properties of hot-pressed NbMo-matrix composites reinforced with ZrB2 particles

The effects of 15, 30, 45, 60 vol% ZrB2 additions on high temperature compression properties of hot-pressed NbMo-matrix were investigated by the compression experiments in the temperature range of 800 °C–1300 °C. ZrB2 particle additions to NbMo matrix could significantly improve the high temperature compressive strength of the composites. The best comprehensive property including strength and ductility belongs to the composites containing 30 vol% ZrB2 with refined grains at the temperature below 1100 °C. The resistant ability to high temperature was directly proportional to ZrB2 content. The compressive strength of composite containing 60 vol% ZrB2 (from 1236.56 MPa to 700.46 MPa) was inversely proportional to temperature. The failure planes of composite containing 15 vol% and 30 vol% ZrB2 were always at angle of 45° to the axis of the compression direction, whereas the failure pattern of composite containing 45 vol% and 60 vol% ZrB2 changed from splitting along the compression direction to cracking at certain angle to the axis of the compression direction with temperature rising.