Phase Coarsening Research Articles

Analytical and numerical modeling of phase coarsening in dense binary systems

The kinetics of phase coarsening in a dense binary, two-phase system were studied theoretically. Existing previous relations are recovered and generalized. Equations for particle size distribution and coarsening are derived in a rigorous way. One of the interesting findings is that the scaling exponent, m, for the kinetics of phase coarsening at ultra high volume fractions takes values in the range 2<m<3, depending on the precise volume fraction of the dispersed phase, when varied over the narrow range 0.9<VV<1. Scaled particle size distributions derived from the current study depend on volume fractions, which is in contrast to Wagner’s particle size distribution for interface-reaction-controlled phase coarsening. The current work substantiates that the kinetics of phase coarsening at ultra high volume fractions, exhibits a blend of both interface-reaction-controlled and volume diffusion-controlled phase coarsening.

Dynamic competition between coarsening mechanisms of Ti2Cu phase during thermal cycling

The dynamic competition between the coarsening mechanisms activates various coarsening behavior of the precipitate in multi-phase metallic materials, leading to different mechanical performances of alloys. In this work, the morphological evolution and coarsening kinetic of Ti2Cu phase in Ti–14Cu alloy were investigated comprehensively during thermal cycling at 200–600 °C. Our results suggest that the coarsening kinetic showed a gradual transition from the Lifshitz-Slyozov-Wagner (LSW) mechanism to the trans-interface diffusion-controlled (TIDC) mechanism. Ti2Cu phases precipitated at the triple junctions of α-Ti matrix by discontinuous precipitation under the control of LSW mechanism at lower temperatures (200–400 °C), and grew into lamellae along the high-energy grain boundaries. While the low-angle grain boundaries within Ti2Cu phase accelerated solute atom diffusion during the coarsening governed by TIDC mechanism at higher temperatures (400–600 °C), which leads to the boundary splitting of lamellae. In addition, it was also found that the blocky Ti2Cu phase improved the yield strength of the alloy as its high solid solution strengthening. This work provides a clear understanding for the coarsening of Ti2Cu phase, it could provide theoretical evidence for the hot working process design to improve the damage tolerance of Ti–Cu alloys.

Perspectives on a Few Puzzles in Phase Transformations: When Should the Farthest Reach the Earliest?

We briefly review the facts concerning two important aspects of phase transitions, namely, critical and coarsening phenomena. A discussion of the universal features, highlighting the current challenges, is provided. Following this, we elaborate on a topic of much recent interest, viz., the Mpemba effect, a puzzle that found mention even in the works of Aristotle. After a description of the debated case of faster freezing of a hotter sample of liquid water, into ice, than a colder one, when quenched to the same subzero temperature, we discuss more modern interest. There one asks, should a hotter body of a material equilibrate faster than a colder one when quenched to a common lower temperature? Within this broad scenario, we focus on magnetic systems. A surprising observation of the effect during the para- to ferromagnetic transition, in a simple model system, viz., the nearest-neighbor Ising model, without any built-in frustration, is described. Some associated future directions are pointed out. A discussion is provided by considering the effect as a kinetic outcome in the background of critical phenomena. A picture is drawn by putting emphasis on the role of spatial correlations in the initial configurations alongside discussing the importance of frustration and metastability in evolution from one state to another. In connection with dynamical freezing, concerning metastability, we have introduced the complex Ginzburg-Landau equation that has relevance in phase transitions, chemical oscillations, and elsewhere. For this model and a few other cases also, we have described how a lack of order or correlation in certain parameters can lead to quicker evolution.

Accelerated coarsening behavior of the γ´-phase in CMSX-4 during non-isothermal heat treatment

In literature, microstructural investigations can be found comparing the evolution of the well-known γ/γ ´ -phase morphology of nickel-based superalloys for long-term heat treatments with and without mechanical load, as well as for isothermal and non-isothermal creep tests. However, data of experiments conducted under non-isothermal conditions without an applied load are hard to find. To close this gap, isothermal and non-isothermal heat treatments without a mechanical load were conducted. Conductive heating was applied to samples that consisted of segments with different cross sections and allowed the simultaneous testing at different temperatures. The microstructural changes were examined by scanning electron microscopy after 500 h and 1000 h. Several established methods for the quantification of the γ ´ -phase coarsening were evaluated and employed for comparison of the two heating conditions studied. The coarsening was more distinct in samples heat-treated under non-isothermal conditions at all temperatures investigated. This was also verified by calculating the connectivity number NA, which was found to be the most useful parameter for quantification of microstructural changes observed. The γ ´ -precipitates became more connected during the heat-treatment, but no preferred direction of coarsening was observed like during rafting under an applied load. Therefore a more general particle agglomeration mechanism is assumed to be responsible for coarsening of the γ ´ -phase.

Effect of Cu-Rich Phase Growth on Creep Deformation of Fe-Cr-Ni-Cu Medium-Entropy Alloy: A Phase Field Study

The Cu-rich phase is a high-efficiency and ultra-stable precipitation-strengthening phase and has been widely used in many steels and alloys, especially in heat-resistant steels and alloys. Creep damage is accompanied with the coarsening of the second phase. In the present work, the calculation of phase diagrams (CALPHAD) method and elastic–plastic mechanics are coupled with the phase field (PF) approach to investigate the growth behavior and the accompanying stress/strain field evolution of nano-sized Cu-rich precipitates in an Fe-Cr-Ni-Cu medium-entropy alloy. The results show that creep strain is intensified with the coarsening of Cu-rich particles. The simulated size of Cu-rich particles is in good agreement previous experimental reports. The plastic strain tends to shear the Cu-rich phase when they are relatively fine (~&lt;11 nm), and the size of the Cu-rich particles has a slight influence on the creep strain at this stage. In contrast, coarse Cu-rich precipitates (~&gt;11 nm) are bypassed by the plastic strain due to the enhancing stress concentration around the interface, and the creep strain is rapidly aggravated with the growth of Cu-rich particles. The coarsening of Cu-rich particles will be retarded by the adjacent particles due to the overlapping of the diffusion zone, and hence the creep strain was reduced when crept for the same time. The retard effect will vanish when their distance is sufficiently long (~&gt;60 nm). When the size of the Cu-rich particles is identical, the creep strain will be mitigated with elongation of the distance between two Cu-rich particles.

Improved creep resistance of 20Cr25NiNb heat resistant steels through grain boundary intermetallic precipitation strengthening

The creep performance of 20Cr25NiNb austenitic steel through the addition of W, Mo, and B elements was investigated. W and Mo enhanced high temperature creep resistance primarily through solid solution strengthening σss and precipitation strengthening σp by introducing Laves phase. Boron enrichment was predominantly observed in Laves phase at grain boundaries (GBs) rather than in σ and G phases. The significant improvement in creep life of B-bearing steel was primarily attributed to a remarkable increase in σp, as trace amounts of B greatly accelerated Laves precipitation at GBs and inhibited σ phase coarsening. The creep resistance decreased significantly after 5000 h thermal aging due to reduced dislocation density, grain coarsening, and decreased solid solution elements in austenite. Creep cracks mainly propagated along GBs, where coarse σ phase provided sites for creep cavity nucleation. The applied stress accelerated σ precipitation and coarsening, resulting in the absence of tertiary creep stage during 4700 h creep of B containing 2025WMoB steel.

Effect of slight Sn modification on mechanical properties and corrosion behavior of Ti- (2–4 wt%) Mn alloys fabricated via powder metallurgy

The addition of Mn to Ti has been extensively investigated due to the remarkable biocompatibility and strength of Ti-Mn alloys, but their ductility was to prove insufficient, particularly for the powder metallurgy technology. In this study, Ti-2Mn, Ti-2Mn-2Sn, Ti-4Mn, and Ti-4Mn-2Sn alloys were manufactured by the powder metallurgy. The impact of slight Sn on the sintering densification, microstructure, mechanical properties, and electrochemical behavior of the Ti-(2–4 wt%) Mn alloys was researched. The findings indicate that a tiny amount of Sn effectively decreased the alloy's melting point, ideal sintering temperature, and sintering time. The addition of Sn didn't transform the lamellar structure of Ti-Mn alloy. In term of Ti-2Mn, Sn favoured the compressibility, played a beneficial effect in encouraging densification and refined the size of α and β phases. The ductility was significantly enhanced (15.9%), strength kept excellent (784 MPa) and corrosion resistance was improved, yielding in achieving a synergistic increase in strength, ductility and corrosion resistance. However, the addition of Sn in Ti-4Mn alloy hindered densification and promoted β phase coarsening, leading to little boost in ductility and deterioration of the corrosion resistance. Those findings could offer new insights to invent low-cost Ti alloys with wonderful performance.

Effects of Long-Term Aging on Structure Evolution and Stress Rupture Property of DD6 Single-Crystal Superalloy

For China’s second-generation aero-engine blade DD6 single-crystal high-temperature alloy, the standard solution-treated test rods were subjected to long-term aging experiments (1290 °C, 1 h + 1300 °C, 2 h + 1315 °C, 4 h air cooling + 1120 °C, 4 h air cooling + 870 °C, 32 h air cooling) at 980 °C for 1000 h, 5000 h, and 7500 h, and the effects of different long-term aging times on the organization evolution, phase precipitation morphology, high-temperature mechanical properties, and endurance performance of the alloy were studied. The results show that with the increase of aging time, the γ′ phase coarsens, joins along the &lt;100&gt; and &lt;010&gt; directions, and merges to form irregularly shaped directional growth and rafting. The endurance life shows a decreasing trend; at 980 °C/243 MPa, 980 °C/270 MPa, 980 °C/309 MPa for the alloys after 5000 h aging, the enduring life decreased by 47.97%, 70.98%, and 76.75%, and 81.25%, 73.18%, and 87.00% after 7500 h aging, respectively. The tensile strength of the alloy at 760 °C first decreases and then increases, with a minimum value at 5000 h; there is a gradual increase in elongation; there is a gradual decrease in tensile strength at 980 °C; and there is first an increase and then decrease in elongation, with a maximum value at 1000 h. This is due to the diffusion phenomenon of the elements in the alloy after 5000 h aging, the emergence of W-rich, Re-, Mo-, and Ni-poor phenomena, and the transformation of the μ-phase from needle-like to rod-like and block-like.

Ageing precipitation sequence and effect of ω and secondary α phases on tensile properties of metastable β Ti-6Cr-5Mo-5V-4Al alloy

The ageing precipitation sequence and the relationship between microstructure and tensile properties of metastable β titanium alloy Ti-6Cr-5Mo-5V-4Al during solution and ageing were investigated. Ageing from 400 to 450 °C, isothermal ω phase (ωiso) precipitated in the alloy, resulting in high hardening and brittle fracture. After ageing at 450–500 °C, ωiso phase was gradually replaced by secondary α phase (αs) with the ageing time increasing. At higher ageing temperature (580–600 °C), ωiso precipitation was suppressed, and αs phase precipitated directly from β phase. The yield strength of sample aged at 450 °C for 12 h was 1368 MPa and the elongation was 5.5% due to ωiso precipitation. The yield strength of sample aged at 600 °C for 12 h was 1108 MPa and the elongation was improved to 15.4% due to the precipitation and coarsening of αs phase.

Inhibiting cracking and improving strength for additive manufactured Al CoCrFeNi high entropy alloy via changing crystal structure from BCC-to-FCC

Hot cracking in laser powder bed fused (LPBF) AlxCoCrFeNi high entropy alloys (HEAs) plague the production of high strength parts. Here we show that the body-centered cubic (BCC) phase with very high hardness (∼670 HV) in LPBF printed AlxCoCrFeNi(x = 1, 0.7) HEAs causes cracking due to the plastic incompatibility between grain boundaries. To mitigate this, we propose a BCC to face-centered cubic (FCC) transformation strategy in the AlxCoCrFeNi HEAs to inhibit cracking and found that the Al0.5CoCrFeNi alloy (i.e., when x = 0.5) with a single FCC crystal structure possess low cracking sensitivity and well intergranular plastic compatibility, accompanied with decreased residual stress confirmed by using X-ray diffraction testing. The mechanical properties of the LPBF printed Al0.5CoCrFeNi HEA can be further enhanced by precipitation heat treatment. Scanning electron microscope/ transmission electron microscopy analysis show that nano-sized B2, L12 and σ phases precipitated from FCC Al0.5CoCrFeNi HEA when aged at 700 °C for 1 h. The ultimate tensile strength (UTS) increases from 899 MPa (as-print) to 1552 MPa (aged) with the elongation decreasing from 35.6 % (as-print) to 7.1 % (aged) due to the Orowan bypass mechanism of nano-precipitates. An increased aging temperature to 800–1000 ℃, decreases the UTS while increases the elongation, accompanied by the L12-to-B2 transformation and B2 phase coarsening. The deformation mechanism is mainly dominated by dislocations and stacking faults in the Al0.5CoCrFeNi HEA sample.

Effects of HIP Process Parameters on Microstructure and Mechanical Properties of Ti-6Al-4V Fabricated by SLM

Ti-6Al-4V titanium alloy products formed by selective laser melting (SLM) are characterized by high strength and low plasticity. In addition, there may be pores inside the material, which may become a fracture sprouting point and accelerate the failure of the parts. Using an optical microscope (OM), scanning electron microscope (SEM), and electronic universal testing machine, the effects of hot isostatic pressing (HIP) parameters on the microstructure and tensile property of SLM-formed Ti-6Al-4V titanium alloy were investigated. The results show that HIP performed below the β-phase transition temperature, and the structure of the Ti-6Al-4V titanium alloy is composed of an α phase and β phase. With the increase in the HIP temperature, the α lath coarsens into a short rod, the content of the β phase increases and coarsens, and the tensile strength and yield strength of Ti-6Al-4V show a decreasing trend. With an HIP process performed at a temperature of 910 °C and pressure of 130 MPa for 2 h, the Ti-6Al-4V titanium alloy obtains the best matching of strength and plasticity.

Retaining multi-oriented and fine grain structure with Ni doping in Cu/Sn-3.0Ag-0.5Cu/Cu transient liquid phase bonding under isothermal aging treatment

Transient liquid phase bonding has been proven to offer exceptional joining strength and dependable high temperature service in chip stacking applications. Nevertheless, conventional Cu/Sn/Cu transient liquid phase bumps had shortcomings, such as smooth phase boundaries and coarsening grains. In this study, the variation of microstructure in Cu/Sn-3.0Ag-0.5Cu/Cu, Cu/Sn-3.0Ag-0.5Cu/Ni, and Ni/Sn-3.0Ag-0.5Cu/Cu transient liquid phase bonds with the sizes less than 10 μm before and after long term aging were investigated. Due to the dissolution of Ni atoms from the substrates at the cold or hot end, the structure exhibited randomly-oriented and small-sized grains. After 1000 h aging treatment, the Ni-containing specimen still retained the abundant grain structure and appeared network-like morphology of Cu3Sn near phase boundaries. Additionally, the shear testing was applied in the aged samples, Ni-doped joints demonstrated better mechanical properties than Ni-free joining. The enhancement of shear strength was attributed to Ni addition, retaining the advantageous grain structure. This present work showed that doping Ni to micro-bumps could halt the deterioration of grain structure over extended usage of electronic devices in 3D-IC technology.

Microstructure evolution and performance of B4C–NdB6 composites fabricated by in situ hot pressing

AbstractB4C–NdB6 composites were fabricated by in situ hot pressing at different temperatures (1950–2150°C) with B4C and Nd2O3 (2–4 wt%) as raw materials. The microstructure evolution of the composites with sintering temperature and Nd2O3 content was studied in detail, and the influence of pressure on the sintering of B4C with different contents of Nd2O3 was also investigated. The performance of the fabricated composites was researched and the toughening mechanism was discussed. The results indicate that Nd2O3 can react with B4C to form the thin‐sheet intermediate products (Nd(BO2)3, Nd2CO5) first, which then transform to band‐shaped NdB6. Pressure can reduce the distance of B4C and Nd2O3, accelerating the mass transfer and contributing to the formation of NdB6. NdB6 and intermediate products are first in agglomerate structure at 1950°C, and then the agglomerates are broken to form dispersive micron and submicron NdB6 at 2000°C by the synergistic function of pressure, diffusion at high temperature, and liquid phase sintering. NdB6 can enhance the densification owing to the bonding function. Excessive Nd2O3 content leads to residual pores, and excessive temperature (2150°C) results in the coarsening of phases. The coexistence of transgranular and intergranular fracture of NdB6 promote the fracture toughness.

Microstructural Characterization of Sn57Bi1Ag Solder Alloy Joints

Sn57Bi1Ag alloy system meets the basic solderability requirements while reliability of solder is less known. The presence of intermetallics that form at the solder-joint interface and in the bulk solder is the primary reason to cause joint failure on simple loading. Furthermore, dissolution of soldered surface (copper, gold, silver, nickel, etc.) into the solder during reflow alters the composition of the interface leading to the formation of intermetallic phases. The present paper addresses the characterization of low temperature Sn57Bi1Ag solder alloy, its joint interface metallurgy and integrity. Generally, formation of intermetallic phases (Cu3Sn, Cu6Sn5, Ag3Sn, AuSn2, Ni3Sn4, etc.) at the solder-pad interface is in the range of 0.3 to 1.0µm. On thermal ageing at 75°C (0.55Tm), the intermetallic phases grow further up to 2.3µm, particularly CuSn and AuSn phases. In addition, to distributed eutectic tin (Sn) and bismuth (Bi) phases, fine eutectic tin and bismuth phases and primary tin (β-Sn) are also observed. Coarsening of Bi and Sn phases is noticed on thermal ageing (75°C and 100°C). The rate of coarsening increases with the supply of thermal energy promoting Sn/Bi atomic diffusion and movement of eutectic boundaries (grain boundaries). However, the Sn-Bi interface is stable without any significant changes in eutectic structures and its morphologies. The mechanical drop test of the Sn57Bi1Ag solder joint passed 120 drops, characteristic life corresponds to the number of drops for a failure of 63.2%. Evaluated as per JESD22-B111 specification to a maximum peak acceleration of 1500G and half-sine shock pulse duration of 0.5 milliseconds, soldered the alloy to copper OSP surface. The solder joint also passed 1200cycles evaluated at -40 to +125°C. Electrical connectivity of the solder joints soldered to ENIG plated test boards is recorded continuously. Crystallographic orientation of Sn and Bi second phases is observed using electron back scattered diffraction (EBSD) of thermal aged solder joints and are also presented in this paper.

Supercritical carbon dioxide assisted phase coarsening of double-percolated polycaprolactone/polystyrene/multi-wall carbon nanotube composites for improved electrical performance and electromagnetic interference shielding

The continuity of conductive network and conductivity performance in double-percolated conductive polymer composites (CPCs) can be improved after static annealing, though, there are often increased viscosities in CPCs when filler contents increased, making annealing process difficult. Herein, the incompatible polycaprolactone (PCL)/polystyrene (PS) systems were designed to double-percolated PCL/PS/multi-wall carbon nanotube (MWCNT) composites, subsequently, thermal and plasticizing effects during carbon dioxide (CO2) annealing were combined to assist phase coalescence. Benefiting from viscosity reduction, phase coarsening, electrical conductivities and electromagnetic interference shielding effectiveness (EMI SE) of PCL/PS/MWCNT composites were promoted even at 5 wt. % filler content. After supercritical CO2 annealing, percolation threshold decreased from 0.50 wt. % to 0.24 wt. %, and EMI SE increased from 31.8 dB to 39.8 dB, which improved 25 %. This work demonstrates phase coarsening of double percolated CPCs is effectively controlled by CO2 annealing conditions, and the final degree of performance improvement is connected to polymer systems.

Effects of cooling manner on Laves phase precipitation and mechanical properties of Al modified super ferritic stainless steels

The solution treating and cooling experiments were conducted to study the microstructure and mechanical properties of Al modified super ferritic stainless steels with various cooling methods. The results demonstrated that the grain was characterized by the stratified distribution. The grain coarsened gradually with the decrease in cooling rate. And the surface grain coarsened obviously, Nb (C, N) particles were precipitated in the samples in different cooling manners. However, the Laves phase was distributed both at the grain boundaries and in the grains in the furnace-cooled specimen, and the area fraction of Laves phase increased significantly with the increase of Al content. With the cooling rate decreased, the yield strength, ultimate tensile strength and Vickers hardness of the Al-free samples increased, while the elongation decreased, and the furnace-cooled specimens showed brittle fracture during the tensile test. The addition of Al also increased yield strength, ultimate tensile strength and Vickers hardness and deteriorated plasticity of samples with different cooling manners. Meanwhile, the plasticity of furnace-cooled samples was more sensitive to addition of Al than water-quenched and air-cooled specimens. The analysis results showed that the plastic deterioration of furnace-cooled samples was mainly related to the coarsening of Laves phase at grain boundaries. Hence, the precipitation of large size Laves phase at grain boundaries should be inhibited in the process of industrial production.

Grain growth inhibition by sluggish diffusion and Zener pinning in high‐entropy diboride ceramics

AbstractThis work reported the grain growth kinetics of high‐entropy diboride (HEB) and HEB‐SiC ceramics containing 10, 20, and 30 vol% SiC during heat treatment at 1800°C. The coarsening of HEB phase occurred in the four kinds of ceramics during heat treatment, especially in HEB ceramics. The kinetic analysis showed that the grain growth of HEB phase in HEB and HEB‐SiC ceramics is controlled by interface‐controlled kinetics and grain‐boundary pinning, respectively. The growth rate constant of HEB grains is lower than ZrB2, which is related to the low grain‐boundary energy and the sluggish diffusion effect in dynamics of high‐entropy materials. The growth rate of matrix phase in HEB‐SiC ceramics is similar to that in ZrB2–SiC ceramics, indicating that the pinning effect of the SiC second‐phase played the dominant role in inhibiting the grain growth of the high‐entropy matrix phase and disguised the sluggish diffusion effect. This study reveals that the grain growth inhibition through sluggish diffusion effect in a high‐entropy ceramic system may be magnified by the possible existence of segregated second‐phase particles located at the grain boundaries.

Strengthening mechanism and corrosion behavior of friction stir welded LAZ933 magnesium-lithium alloy

In this study, friction stir welding (FSW) technique was applied to the LAZ933 magnesium-lithium (Mg-Li) alloy. Microstructure, mechanical properties and corrosion behaviors of friction stir welded LAZ933 magnesium-lithium alloy were analyzed by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffractometry (XRD), transmission electron microscopy (TEM), hardness, tensile, and electrochemical test. The experimental results indicated that FSW resulted in significant refinement of β phase, reduction of α phase content as well as dissolution of Mg17Al12 and AlLi (γ) precipitates in the nugget zone (NZ). The generated MgLi2Al (θ) precipitates in the NZ and heat-affected zone (HAZ) which had a coherent structure with the matrix could significantly strengthen the Mg-Li alloy. The ultimate tensile strength of the joint reached 163.5 MPa, and elongation reached 15.21%. In the weakest area of the weld (HAZ), the strengthening caused by the solid solution of α phases and formation of θ precipitates compensated the strength loss induced by the phase coarsening by thermal exposure in FSW, resulting in the joint fractured in the base metal (BM) and showed a ductile pattern. The corrosion current density changed from 4.831 × 10−5 A/cm2 to 2.054 × 10−5 A/cm2, which indicated that the weld had better corrosion resistance than the BM.

Microstructure and mechanical properties of the new cladding austenitic stainless steel of 15–15Ti–Y after aging at 500–700 °C for up to 1000 h

As a promising material for fuel cladding, 15Cr–15Ni–Ti (15-15Ti) austenitic stainless steel is widely used in core materials of nuclear reactors due to its excellent creep and oxidation resistance. To further enhance the stability of 15–15Ti steel in ultra-long service time at high temperature, the yttrium-modified 15Cr–15Ni–Ti (15-15Ti–Y) was aged at 500 °C, 600 °C and 700 °C for up to 1000 h. The grain size and precipitation behavior including precipitates species, morphology, quantity, formation sequence and location were systematically investigated. Through the detection and analysis of electron backscatter diffraction, scanning electron microscope, X-ray diffraction and transmission electron microscope, the results indicates that Y is a strong solute segregation element, which hinders the formation and coarsening of M23C6 phase along the grain boundary, thus facilitating the formation of fine intragranular precipitation. At the same time, the addition of Y inhibits recrystallization, grain growth and intergranular precipitation, and promotes intragranular precipitation. Therefore, after aging at 500 °C for 1000 h, the Chib particles only precipitated in 15–15Ti–Y steel, while the size of precipitates in grains interiors and area fraction of M23C6 phase along grain boundaries in 15–15Ti–Y steel were always smaller than that of 15–15Ti steel. Besides, the effect mechanism of Y addition on precipitation behavior and mechanical properties of 15–15Ti–Y after aging is also discussed. The comparison shows that the hardness of the two steels has little change after aging, but the Charpy impact toughness and tensile properties have decreased to varying degrees. As the main reason affecting the mechanical properties, the intergranular precipitation in the chain after low temperature aging weakens the impact toughness of 15–15Ti, while the fine intragranular precipitation after high temperature aging can improve the strength of 15–15Ti–Y. Therefore, compared with 15–15Ti steel, 15-15Ti–Y steel shows higher hardness, impact toughness and uniform elongation after aging at 500–700 °C for 1000 h.

Influence of Al doping and annealing on the microstructures and electrical properties of CrSi films prepared by magnetron co-sputtering

In this work, we prepared CrSi films with different Al contents by DC magnetron co-sputtering, and studied the effect of Al content and annealing temperature on the microstructure and electrical properties of the films. The temperature coefficient of resistance (TCR) of the films increases with increasing Al content. Furthermore, the TCR gradually changes from negative to positive value with the increase of the annealing temperature, and reaches zero at a critical temperature. When the Al content is lower than 3.06 at.%, the TCR is always negative after annealing. An excellent combination of high sheet resistance of 5.36 kΩ/sq with near zero TCR of −10.07 ppm/°C were achieved in the films with an Al content of 3.87 at.% after annealing at 520 °C. The stability and crystallinity of the film are improved by the addition of Al element. The mixture of amorphous and crystalline phases results in a near zero TCR. Moreover, the coarsening of the crystalline phase and the increase in spacing of the crystalline phase induces the increase of sheet resistance.