High-strength Alloys Research Articles

Effect of rolling-texture intensity on fretting damage and subsurface deformation behavior in a high-strength titanium alloy

Fretting damage is common in the high-strength titanium alloy fastener widely used in the aeronautic industry, leading to the failure of fastening fit or the initiation of crack. The titanium alloy fasteners often have typical preferred orientation characteristics (i.e., texture), and this is one of the important factors affecting its performance. However, the investigations on the mechanism of β rolling-texture intensity on fretting damage resistance and subsurface deformation are less addressed. Hence, fretting wear tests were carried out on samples with different rolling texture intensities. The results demonstrate that the samples with quite low (A-10 % sample) and quite high (D-70 % sample) rolling-texture intensity both exhibit excellent fretting wear resistance, but their mechanisms are completely different. Uniformly dispersed grain orientation renders the A-10 % sample with good recovery ability and a positive friction effect during wear. Low stress only concentrating at grain boundaries (GBs) weakens cracks’ initiation and propagation. The unique orientation-layered structure (OLS) leads to excellent recovery ability and a positive friction effect. Crack propagation is inhibited and only propagates along the OLS boundary without a connected trend. However, samples with moderate rolling texture intensity exhibit severe wear. Dislocations are restricted in local areas, so the poor recovery ability makes them have a negative friction effect. Crack propagation driving force continuously increases. Appropriate rolling texture intensity can reduce wear by three times. This study can provide information on the principle for designing fretting damage-resistant alloys.

Excellent strength-toughness combination of NiAl–30Cr composites with novel in situ composite microstructure containing NiAl matrix and Cr single-phase

Lightweight NiAl alloys are expected to replace high-density nickel-based superalloys, but their mechanical performance needs to be improved. In this work, NiAl–30Cr composites with a novel heterogeneous microstructure composed of fine NiAl matrix and Cr single-phase was successfully prepared. Nanoscale Cr particles with 15 nm in size precipitated in NiAl matrix are coherent with NiAl matrix owing to very low interplanar and interatomic spacing mismatch. Such a composite microstructure makes NiAl–30Cr exhibit high strength and high toughness. The yield strength (1207 MPa), ultimate compressive strength (2307 MPa), product of strength and plasticity (29.3 GPa%), and fracture toughness (10.76 MPa m1/2) of NiAl–30Cr increased by 96.6%, 85.6%, 55.1% and 19.7% respectively at room temperature compared to the corresponding ones of NiAl. At 1000 °C, the yield strength (144 MPa) of NiAl–30Cr was 85.9% higher than that of NiAl. Solution strengthening and precipitation strengthening were the key strengthening mechanisms at room temperature. The enhancement in toughness was attributed to grain refinement, increased crack propagation paths, weakened Ni–Al covalent bonding and coordinated deformation of Cr single-phase and NiAl matrix. By contrast, the main strengthening mechanism at 1000 °C is the solid solution Cr atoms hindering dislocation climbing and the stable interface bonding between the Cr nanoprecipitation phase and the NiAl matrix. This work provides new ideas for preparing high-strength and tough NiAl alloy.

A Stochastic Dynamics Method for Time-Varying Damping Depending on Temperature/Frequency for Several Alloy Materials.

In the field of aerospace and advanced equipment manufacturing, accurate response analysis has been paid more attention, requiring a more comprehensive study of the variation of mechanical parameters with the service environment. The damping variation characteristics of 304 aluminum alloy, Sa564 high-strength alloy, GW63K magnesium alloy, and Q235 steel were investigated in this paper, which plays a significant role in the dynamic responses of structures. Variable damping ratios were revealed by the damping tests based on a dynamic mechanical analysis (DMA). The numerical method of temperature/frequency-dependent damping parameters in stochastic dynamics was focused on. With a large variation in the damping ratio, a numerical constitutive relation for temperature-dependent damping was proposed, and an efficient stochastic dynamics method was derived to analyze the responses of structures based on the pseudo excitation method (PEM) and variable damping theory. The computational accuracy and validity of the proposed method are confirmed during the vibration tests and numerical analysis. Based on the comparison results of the two damping models and the experiments on GW63K alloy, we proved that the proposed method is more accurate to the real response of the actual engineering structure. The differences in dynamic responses between the constant damping and experiments are significant, and more attention should be paid to the numerical method of stochastic dynamic response of variable damping materials in the aviation and aerospace fields and high-temperature environments.

Study on the microstructure and mechanical properties of VW73B alloy at high extrusion ratio

The microstructure and mechanical characteristics of VW73B prepared by a high extrusion ratio (70:1) were studied. High-strength plastic VW73B alloy containing long-period structural phase (LPSO) was obtained by extrusion process. OM, SEM, TEM, and EBSD were used to investigate the relationship between microstructure and mechanical characteristics of VW73B. The findings indicate that VW73B presents complete dynamic recrystallization after deformation, and there are 14H-LPSO phases, SFs, and a large amount of β´ phase, which are precipitated after aging treatment. The UTS, YS, and EL of VW73B in peak aging state are 406 MPa, 339 MPa, and 9%, respectively. The β´ phase, LPSO phase, poor texture, and fine grain strengthening of VW73B contribute to its exceptional characteristics.

Fabrication of architecturally designed steel for improving isotropy of mechanical properties using directed energy deposition

As an excellent illustration of architectural alloy designs, multilayered structures, which incorporates high-strength and high-ductility alloys in their layered composition, can accomplish unusual combinations of strength and ductility. This is possible because the continuous microstructure consisting of a single phase without a phase boundary in each layer results in a uniform distribution of strain. However, the multilayered structure shows anisotropic mechanical properties due to discontinuity from the phase boundary in the perpendicular direction (z-direction). In this work, an alloy system with a 3D continuous microstructure with two distinct steels was manufactured using laser-based directed energy deposition. The alternately deposited lines of two distinct alloys, along with the rotated consecutive layers, contribute to creating a woven-like structure. This architectural structure features continuous microstructures in multiple directions. Successfully manufactured both multilayered and woven-like systems demonstrated advanced yield strength and uniform elongation compared to each constituting alloy in the xy plane. In the z-direction, however, only the woven-like system exhibited improved properties as in the xy plane; the multilayered system did not. This isotropy in the mechanical properties of a woven-like system results from a 3D continuous microstructure in the z-direction. The strain analyses confirmed the deformation of the brittle body-centered cubic phase and partitioning to the ductile phase which are key mechanisms of mechanical property enhancement with continuous microstructure.

Additively manufactured copper alloy with heterogeneous nanoprecipitates-dislocation architecture for superior strength-ductility-conductivity synergy

Employing a single strategy that overcomes the strength-ductility-conductivity trade-off in copper alloys has proven to be challenging. In this study, we introduced a novel heterogeneous nanoprecipitate–dislocation (HND) architecture in CuCrNb alloy consisting of a multi-modal core–shell grain structure and an interconnected dislocation network pinned by abundant nanoprecipitates. Our CuCrNb-HND alloy exhibited superior strength–ductility synergy at both room and elevated temperatures. In particular, aging treatment-induced high-density coherent Cr secondary nanoprecipitates into the HND skeleton endowed the CuCrNb-HND450 alloy with a high tensile strength of over 1 GPa and a conductivity of ∼50%, surpassing those of most of the reported additively manufactured copper alloys. An in situ transmission electron microscopy heating experiment revealed the superior thermal stability of the HND architecture. Hierarchical strengthening contributed to the enhancement of mechanical properties. At the micrometer scale, the harmonic grain structure with a strong fine-grained shell and a ductile coarse-grained core effectively improved mechanical properties by suppressing localized plastic deformation. At the nanometer scale, the synergistic effect of the nanoprecipitate–dislocation network further improved the alloy strength by slowing down dislocation movement. Overall, our proposed HND architecture provides an efficient pathway for developing high-strength and high-conductivity copper alloys.

Strength and ductility improvement of the axial gradient microstructure TC21 titanium alloys manufactured by electropulsing plus step-quenching treatment

In order to reduce the weak area caused by traditional connection method and improve the structural efficiency of aircraft, the design concept of an integral component with dual microstructure is proposed. The electropulsing treatment (EPT) was used to produce an axial gradient microstructure (AGM) in TC21 titanium alloy, followed by the step-quenching treatment (SQT) to tailor the precipitation behavior of the α phase. Results demonstrate that the AGM produced by the combination of EPT and SQT achieves a simultaneous enhancement in both strength and plasticity of the alloy. Compared to EPT alone, the SQT results in the dissolution of the bimodal microstructure region with small-sized α phase, and an increased density of secondary α phase precipitation in both the transition and lamellar microstructure regions. During room temperature tensile deformation, coordinated distribution of deformation occurs sequentially in various regions, the 101̅0112̅0type of prismatic slip and deformation nanotwins exist in the equiaxed and lamellar α phase, respectively. Moreover, the deformation gradually declines from the bimodal region to the lamellar region, leading to the fracture of AGM in the bimodal region and an overall augmentation of the strength and plasticity of TC21 alloy. Hence, the results of this paper can provide research basis for the strength and plasticity improvement and deformation damage mechanism of high strength and toughness titanium alloy.

Comparison of turning process performance using modified cutting inserts under minimum quantity lubrication

ABSTRACT While machining of high-strength alloy steel materials, poor surface quality and decreased tool life are result by an increase in the cutting zone temperature close to the machining region. To overcome this, surface texture with green manufacturing environment is an alternate path to enhancing machining performance. In the present work, novel Parallel Grooved Textured Tools (PGT) was developed and studied the performance of so developed tools. Further, the Untextured Tool (UT) and PGT performance was compared while machining EN24 alloy steel under Minimum Quantity Lubrication (MQL) condition. It was perceived from result that textured tools reduced the cutting temperature (CT), rake wear (RW), flank wear (FW), surface roughness (Ra) and cutting force (CF) up to 18.96%, 18.79%, 24.31%, 12.69%, and18.96% respectively compared to UT.

Development of a New High Strength Alloy from Low Alloy Steel Wire by Innovative Additional Cold Wire Feeding Used in Wire Arc Additive Manufacturing

Development of a New High Strength Alloy from Low Alloy Steel Wire by Innovative Additional Cold Wire Feeding Used in Wire Arc Additive Manufacturing

Atomistic study on effects of solute atoms on energy profile of edge dislocation mobility in FCC-Cu alloys

Solid-solution strengthening is an effective method to increase the mechanical strength of metal alloys. Revealing the solid-solution strengthening mechanism based on the energy profile of the dislocation motion is vital for the non-empirical development of high-strength metal alloys. This study provides detailed energy profiles (i.e., energy surfaces) of the edge dislocation gliding motion under the effect of solute atoms, as well as the atomic-scale origin of solute strengthening in face-centered cubic (FCC) Cu alloys. The maximum shear stress (τmax) required for the dislocation to leave the solute atoms (Ni, Co, and Mo, all with different sizes and stacking fault effects) was qualitatively evaluated by finite temperature molecular dynamics simulations. By the nudged elastic band (NEB) analysis, we determined the atomistic origin of the energy barrier for the edge dislocation motion and the maximum force required to overcome the solute pinning effect (i.e., depinning force, FNEB) in binary Cu alloys. By linking FNEB to the size misfit, a theoretical prediction model based on size effects and the volumetric strain field was used and can qualitatively explain the increment in the maximum shear stress (Δτmax) by the solute atoms. These results provide an atomistic basis for the prediction of the solute-strengthening effect correlated with the edge dislocation motion in wide FCC systems.

Microstructure and Mechanical Properties of Al-Li Alloys with Different Li Contents Prepared by Selective Laser Melting.

Research on the development of new lightweight Al-Li alloys using a selective laser melting process has great potential for industrial applications. This paper reports on the development of novel aluminum-lithium alloys using selective laser melting technology. Al-Cu-Li-Mg-Ag-Sc-Zr pre-alloyed powders with lithium contents of 1 wt.%, 2 wt.% and 3 wt.%, respectively, were prepared by inert gas atomization. After SLM process optimization, the microstructure and mechanical properties of the as-printed specimens were investigated. The densifications of the three newly developed alloys were 99.51%, 98.96% and 92.01%, respectively. They all had good formability, with the lithium loss rate at about 15%. The as-printed alloy with 1% Li content presented good comprehensive properties, with a yield strength of 413 ± 16 MPa, an ultimate tensile strength of 461 ± 12 MPa, and an elongation of 14 ± 1%. The three alloys exhibited a layered molten pool stacking morphology and had a typical heterostructure. The columnar crystals and equiaxed fine grains were alternately arranged, and most of the precipitated phases were enriched at the grain boundaries. The change in Li content mainly affected the precipitation of the Cu-containing phase. When the Li content was 1 wt.%, the following occured: θ phase, T1 phase and TB phase. When Li increased to 2 wt.%, T1 and T2 phases precipitated together. When Li reaches 3 wt.%, δ' phase precipitated with T2 phase. This study provides useful guidance for the future SLM forming of new crack-free and high-strength Al-Li alloys.

Tool life assessment of high strength cast iron alloys in dry face milling operations

The advancement in cast iron alloy properties has led to more efficient materials, especially in the automotive industry. However, this progress has also increased the demand for more durable tools with greater resistance to cutting operations. Conducting an in-depth investigation into the impact of these materials on tool lifespan is crucial, as it directly affects productivity. The main objective of this study was to analyze the lifespan of uncoated cemented carbide tools during milling operations using four high-strength cast iron alloys under various dry cutting conditions. A full factorial Design of Experiment (DoE) (23) was employed. The input variables included cutting speed (vc) of 230 and 350 m/min, tool feed (fz) of 0.1 and 0.2 mm/tooth, and materials, namely cast irons (FC 250, FC 300(Mo), FC300(Mo+RG), and FV 450). Additionally, material tests were conducted on billets without holes to simulate mild cutting conditions and with holes for more severe machining conditions. The established machining operation was face milling without cutting fluid, with the axial depth of cut (ap) and radial depth of cut (ae) maintained constant at 1 mm and 60 mm, respectively. The results showed that FV 450 had the shortest tool life, as expected for the hardest and resistant material, with a maximum lifetime difference of 83 % less when compared to FC 250, the softest one that had the longest tool lifespan. The introduction of holes also significantly reduced the overall tool life by about 57 %. The findings highlight the importance of factors such as cutting speed, feed per tooth, material composition, impact, and workpiece surface quality, which significantly influence tool performance.

Multiscale microstructure containing nanometer-scale precipitations and stacking faults yields a high-strength Al-5Cu alloy by electron beam freeform fabrication

Electron beam freeform fabrication (EBF3) additive manufacturing technique has been successfully employed to print the non-weldable Al-5Cu thin-walled parts through an optimized set of process parameters. Post-heat treatment is conducted to engineer the desirable microstructure containing multiple nanostructures, i.e., the nanoscale θ" and θ' precipitates, stacking faulted zones and Al-Cu-Cd clusters, leading to a high-strength Al-5Cu alloy with good ductility. The grain formation mechanisms are revealed via a combinatorial simulation and experimentation. It is shown that EBF3 process can produce three different types of grain microstructures: fully equiaxed, fully columnar, and the mixture. In the layerwise melt pool solidification process, wide partially melted zone is observed to favor the formation of equiaxed grains due to its inheritance characteristic. After solution and aging heat treatment, Al-Cu-Cd nanoclusters (∼ 2 nm in Dia.) are generated, which facilitates the formation of nanoscale stacking faulted zones (∼11 nm). Meanwhile, as heterogeneous nucleation sites, Al-Cu-Cd nanoclusters effectively promote θ'-Al2Cu phase (∼ 19 - 114 nm) precipitation to enable the coexistence with fine θ"-Al3Cu precipitates (∼ 7 - 37 nm). The multiscale microstructure, especially incorporating the newly identified nanoscale stacking faulted zones, activates multiple strengthening mechanisms. Consequently, its tensile properties at room temperature reach an ultimate tensile stress of ∼ 496.5 MPa, yield strength of ∼ 435.7 MPa, and elongation of ∼ 9.6%, which are superior to other as-cast and additively manufactured Al-Cu alloys. This work offers a promising processing route to directly fabricate high-strength near-net-shape Al-Cu alloy parts for the aerospace and automotive industries.

Stress Corrosion Cracking of High-Strength Ni-Base Alloys in Pressurized Water Reactor Primary Water Containing KOH vs. LiOH

The stress corrosion cracking (SCC) behavior of high-strength Ni-base Alloys X-750 and 718 has been investigated to assess the effect of replacing LiOH with KOH as the pH moderator in pressurized water reactor (PWR) primary circuit coolant. The SCC initiation behavior of X-750 was evaluated by multitensile specimen constant load test in either LiOH- or KOH-containing PWR primary water. The SCC growth behavior of X-750 and Alloy 718 was evaluated on compact tension specimens with on-the-fly changes between LiOH- and KOH-containing water in three different PWR primary water chemistries. Direct current potential drop technique was used for in situ monitoring of crack initiation time and crack extension in SCC initiation and propagation tests, respectively. The results suggest no significant effect of KOH vs. LiOH on the SCC initiation or propagation of the tested materials.

Effects of grain orientation and grain size on etching behaviors of high-strength and high-conductivity Cu alloy

Etching is a precise chemical material reduction processing method that can get small and precise components with specific size and pattern. In etching of the high-precision lead frames, microstructure of the Cu alloy plate has become an important factor that affects the etching rate, size accuracy and surface roughness of the etched products. In this study, the CuCrSn alloy samples with different grain size were etched by aqua regia and then comprehensively characterized to reveal the effects of grain orientation and grain size on the etching behavior. The results show that the etching morphologies and rates of the Cu alloy grains are significantly different and dominated by the grain orientation, and etching of the grains with their surface nearly parallel to the {100} crystal planes are the lowest, meanwhile the roughness of these etched surfaces is the lowest. After the etching, the grain surfaces show very fine stepped structures composed of two or more {100} crystal planes along which the Cu atoms dissolve. The priority corrosion is prone to occur at the grain boundaries (GBs), and the etching around the GBs is more significant when the grains are finer. With the increase in grain size, the etching at the GBs become less apparent, and the difference in etching rates between different grains increases, results in height difference and an increase in roughness of the etched surfaces.

Effect of Zr addition on the microstructure and mechanical properties of hot-rolled TiZrAlSn alloys

In this study, the microstructure and mechanical properties of hot-rolled χZr-Ti-5Al-2.5Sn (χ = 0, 10, 20, 30 and 35, wt%) alloys were systematically investigated. With the increase of Zr addition, phase constitutions of TiZrAlSn alloys change from single α phase to α + α´, α´ and α´ + αʺ + β phases in sequence while the β transformation temperature decreases. A lower content of α”+β phases appears in the 35Zr-Ti-5Al-2.5Sn alloy. The yield strength of TiZrAlSn alloys increased monotonically from 612 ± 15 MPa for basal Ti-5Al-2.5Sn alloy to an ultra-high strength of 1386 ± 11 MPa for 35Zr-Ti-5Al-2.5Sn alloy, which is ∼126% higher than that of basal alloy. The high content of Zr solute atoms, high density of dislocations and interfaces/boundaries in α´ martensite phase render the ultra-high yield strength and high strain hardening rate in 35Zr-Ti-5Al-2.5Sn alloy. With respect to ductility, the uniform and total elongations increase initially from Ti-5Al-2.5Sn alloy to 10Zr-Ti-5Al-2.5Sn alloy and decrease afterward until 35Zr-Ti-5Al-2.5Sn alloy. The bimodal microstructure of primary α grains and secondary α´ martensite (βtrans region) rendered 20Zr-Ti-5Al-2.5Sn alloy the best comprehensive mechanical properties which included the tensile strength of 992 ± 11 MPa, total elongation of 17.2 ± 1% and a high strain hardening rate. This high strain hardening ability of 20Zr-Ti-5Al-2.5Sn alloy comes from the compatible deformation of soft primary α and hard secondary α´ martensite phases with high density of dislocations and boundaries. In addition, the 20Zr-Ti-5Al-2.5Sn alloy shows a high elongation during tensile necking. The corresponding ductile fracture morphologies of TiZrAlSn alloys are also analyzed. These high-strength TiZrAlSn alloys could be helpful for developing novel TiZr alloys with a high strength and ductility.

A comparative experimental study of different magnetic field intensities on electrical discharge turning of EN24 steel alloy

This comparative study investigates the effect of various magnetic field (MF) intensities on the precision machining of cylindrical workpiece of EN24 Steel alloy in the electrical discharge turning configuration. EN24 steel is a high-strength alloy commonly employed in aerospace, automotive, and general engineering applications. The objective of this research is to evaluate the impact of MF intensity on the material removal rate (MRR), tool wear rate (TWR), overcut (OC), and surface roughness ( Ra). The rotational speed of the workpiece, peak current, and pulse-on time were kept constant machining parameters throughout the experiments. The experimental results reveal that increasing MF intensity enhances MRR, OC, and surface finish. However, it is observed that higher MF intensities lead to an elevate TWR which was a negative effect on machining performance. SEM analysis was conducted on the machined surface, revealing that higher magnetic intensity resulted in the formation of a reduced recast layer and remelted debris. The findings were further supported by energy-dispersive spectrum results, which indicated a lower presence of oxide and carbide formations on the machined surface when subjected to higher MF intensity.

First-principles study on the high-strength and high-conductivity modification mechanism of C7035 copper alloy by Ni, Si, and Co solid solution

In order to investigate the effects of matrix solid solution, precipitate phases, and microscale interfaces on the mechanical and electrical properties of copper alloys, we employed first-principles calculations based on density functional theory study aimed to understand how alloying elements enhance the strength and conductivity of copper. The results demonstrated that doping Co atoms into the copper matrix using the Dop2 structure model exhibited the most significant improvement in both mechanical and electrical properties. The Young's modulus was doubled compared to pure copper, and the hardness increased several times. The electrical conductivity reached 59.8 % of the International Annealed Copper Standard (IACS), showing a 6.6 % enhancement compared to Si doping. To validate computational results, we conducted experiments that confirmed the accuracy of the predicted mechanical and electrical properties. Furthermore, the introduction of Co effectively reduced electron losses at the interface between the precipitate phase and the copper matrix. The electron transmission rate through the Co2Si (211)/Cu (111) interface reached 78.6 %, representing a 94.1 % improvement compared to the Ni2Si (111)/Cu (111) interface. In conclusion, Co can simultaneously enhance the mechanical and electrical properties of Cu–Ni–Si alloys, providing theoretical guidance for the design and fabrication of high-strength and high-conductivity copper alloys.

A roadmap for tailoring the microstructure and mechanical properties of additively manufactured commercially-pure titanium

In recent years there has been a growing interest in using additive manufacturing to produce near net-shape parts from titanium alloys. Most of these studies have focused on the fabrication of various high-strength alloys such as Ti5553 and Ti–6Al–4V, but there is also a desire to produce parts out of lower-strength and higher elasticity alloys such as commercially pure titanium (CP–Ti). In this work, we have shown the effects on various properties of CP-Ti Grade 2 produced via the Laser Powder Bed Fusion (L-PBF) manufacturing process and subsequent heat treatments. Samples with 99.98 % density were produced. Microstructure and phase evolution was characterized by X-ray and electron backscatter diffraction and polarized light microscopy. Oxygen was found to be incorporated during manufacture and processing by Inert Gas Fusion (IGF). Heat-treatment of the samples resulted in recrystallization of the acicular microstructure. By testing the mechanical properties throughout the recrystallization temperatures, it was observed that the grain recrystallization lead to a reduction in mechanical strength without a significant improvement in ductility, therefore making a low temperature heat-treatment that retains the AM microstructure an interesting alternative to strengthen CP-Ti.

Multi-objective optimisation of process parameters for laser-based directed energy deposition of a mixture of H13 and M2 steel powders on 4Cr5Mo2SiV1 steel

ABSTRACT In present paper, a universal method for multi-objective parameter optimisation of additive manufacturing processes was proposed and successfully applied to laser-based directed energy deposition (DED) experiments with mixtures of H13 and M2 steel powders that were deposited on 4Cr5Mo2SiV1 hot work die steel. The DED experiments were designed and completed based on the response surface method with 13 groups of laser parameters. The microstructure of the deposited alloy steel was observed and its mechanical properties were tested. The deposited steel alloy achieved an ultimate tensile strength (UTS) of 1821 ± 30 MPa with a reasonable elongation of approximately 4.5%, and the bond strength specimens achieved a bond toughness of ∼10.66% with a moderate UTS (1329 ± 28 MPa). A multi-objective optimisation method was proposed based on response surfaces which were established according to microstructural characteristics and mechanical properties data. It provided a basis for achieving high strength or high toughness DED-fabricated steel alloys.