Mechanical Properties Of Metallic Materials Research Articles

Restoration of exceptional mechanical properties of Al–Cu–Li (AA 2198) alloy post-friction stir processing by recovery of T1 precipitates through controlled temper conditions

Friction stir processing (FSP) is considered to be an effective technique to improve the mechanical properties of metallic materials through grain refinement. However, the fine-grained Al–Cu–Li (AA2198) alloy exhibits a drastic reduction in strength post-FSP as compared to its peak aged temper condition due to the dissolution of its primary strengthening phase, T1 (Al2CuLi) during processing. The present study is aimed at recovering T1 precipitates, thereby restoring the alloy strength. The evolution of microstructure in both the base alloy and FSP alloy subjected to different temper conditions was examined by detailed electron microscopy and was analyzed through a differential scanning calorimetry study. The mechanical properties of the alloy were evaluated by Vickers hardness measurements and tensile testing at room temperature. Experimental findings reveal that the direct aging treatment is ineffective in recovering T1 in FSP alloy due to the delayed precipitation kinetics. However, prior cold working led to the recovery of substantial amounts of T1 during further aging of the FSP alloy. The variation in hardness and tensile properties were in alignment with the precipitation states, and the exceptional mechanical properties were restored in the FSP alloy with the recovery of T1 by cold work prior to aging. The strength modeling indicated that the experimental yield strength after T1 recovery is lower than the predicted value, and these are attributed to the incomplete recovery of the T1 due to trapping of the solute in Cu-rich Al based intermetallics. To dissolve the intermetallics solution treatment was performed after FSP, but it led to significant abnormal grain growth (AGG) and is analyzed using Humphrey’s framework.

Experimental study and finite element modelling of pure copper tube fabrication via the Parallel Tubular Channel Angular Pressing (PTCAP) Process

The Parallel Tubular Channel Angular Pressing Process (PTCAP) has emerged as a promising method for refining the grain structure and enhancing the mechanical properties of metallic materials through severe plastic deformation. This study focuses on a comprehensive investigation of the PTCAP process, combining experimental and numerical analysis to gain insights into its underlying mechanisms. Experimental investigations involve processing a commercially pure copper tube using PTCAP under controlled conditions. In parallel, an explicit numerical analysis is developed using ABAQUS software to simulate the deformation behavior during PTCAP. The model incorporates material constitutive equations and accounts to describe the material response under high strain rates and large deformations. The research aims to investigate how multi-pass PTCAP affects hardness, strain homogeneity, and stress distribution. A comparison between the load punch from the experimental and FEM is conducted to validate the FEM results, and there is a good correlation between both. Hardness measurements are conducted at various stages to quantify the changes in material hardness resulting from the successive PTCAP passes. The hardness of the Cu tube increased by 63.45, 94.51, 103.98, and 105.64% after 1 to 4 passes, respectively.

RESEARCH ON THE INFLUENCE OF SECONDARY HEAT TREATMENT PARAMETERS ON THE MARTENSITIC STAINLESS STEEL PROPERTIES

Heat treatments constitute an essential stage for the possibilities of improving the mechanical properties of metal materials, such as hardness, mechanical strength and corrosion resistance. Any change in the heat treatment parameters, such as temperature, holding time and cooling rate, can influence the structure of the steel and cause the formation of the martensitic phase, responsible for increasing the hardness. Moreover, if the temperature and time are correctly selected, they can help eliminate internal stresses and imperfections in the crystalline structure, thus improving the strength and ductility of the steel. The hardness of martensitic stainless steel needs to be increased to meet the performance requirements for the applications in which it is used, such as the manufacture of knives, surgical instruments or components for the aerospace industry. Martensitic stainless steel is valued for its corrosion resistance and relatively low cost, and the hardness increase is essential to ensure proper operation and durability of products manufactured from this material. Any change in the martensitic stainless steel heat treatment parameters has a significant impact on increasing the hardness and improving its mechanical properties, being essential for obtaining the desired performance in various industrial applications.

Tuning generalized planar fault energies to enable deformation twinning in nanocrystalline aluminum alloys

As deformation twins have a profound impact on the plastic flow and mechanical properties of metallic materials, enhancing deformation twinning in face-centered cubic (FCC) metallic materials has long served as a unique microstructure design strategy to attain an extraordinary strength-ductility synergy. Deformation twinning, however, rarely occurs in pure FCC Al and its alloys since its generalized planar fault energies (GPFEs) are almost unaffected by most soluble alloying elements such as Mg, Zn and Cu. Here we successfully tune the GPFEs of a nanocrystalline Al-Mg alloy by alloying with Zr, Fe or Y element, and enable deformation twinning in the Zr-, Fe- and Y-containing alloys. Based on a combined analysis of microscopic observations, modeling and ab initio calculations, we find a strong grain-size-dependent twinning (i.e., twinning occurs in preferable grains having sizes in the range ∼20–40 nm), as well as only one single twinning plane (i.e., twinning occurs in single, parallel atomic planes) for twin formation rather than intersecting twinning planes (i.e., twinning occurs in multiple, unparallel atomic planes) usually observed in coarse-grained FCC materials. This interesting twinning behavior is further observed to be accompanied by grain rotations, producing defective twin boundaries. Our experimental results extend the current understanding of the plastic deformation mechanisms in nanograined metallic materials, and will guide microstructure design of twinnable nanograined Al alloys with an improved strength-ductility synergy.

Cross-sectional geometry effect on bending strength of gold micro-cantilever with trapezoidal cross-section

Gold is a promising material for movable components in MEMS devices by the high mass density, which allows reduction of the Brownian noise. Mechanical properties of metallic materials are known to be affected by the sample size effect. When bending test is utilized, the sample geometry effect is another factor. In this study, effects of the shape of the cross-section, or the cross-sectional geometry effect, are evaluated using micro-cantilevers with a trapezoidal cross-section. The yield stresses are ranged from 112 MPa to 185 MPa in micro-cantilevers composed of single crystalline gold, and the yield stresses varied from 372 MPa to 489 MPa in polycrystalline gold micro-cantilevers. The yield stress is found to be higher in the micro-cantilever having a smaller ratio of the top width over the bottom width, which demonstrates the cross-sectional geometry effect. Also, the cross-sectional geometry effect is more significant in the polycrystalline micro-cantilevers.

Magnetic-assisted ultrasonic nanocrystal surface modification induced microstructures of titanium alloy

Surface nanocrystallization together with compressive residual stresses can significantly improve the mechanical properties of metallic materials. An innovative surface process called magnetic-assisted ultrasonic nanocrystal surface modification (MA-UNSM) is reported here. By coupling integrates magnetoplasticity and shocking-induced plasticity, the MA-UNSM can enhance the plastic deformation capability of materials without significantly increasing the USNM processing temperature, thus realizing more effective grain refinement, deeper plastic-affected depth and higher-magnitude residual stresses, as evidenced by microscopic characterization and mechanical measurements. Our results demonstrated that the magnetic field improves the plasticity of the material by reducing the resistance between dislocations and pinning obstacles and thus enhances the effectiveness of ultrasonic peening treatment. Magnetic field with two intensities (0.25 T and 0.6 T) were used to assist UNSM, and the results showed that 0.6 T was the better condition.

Effective characterization for the dynamic indentation and plastic parameters acquisition of metals

As a fundamental test technique for the mechanical properties of materials, indentation shows broad application prospects. Compared to the well-studied quasi-static indentation, relatively few and incomplete studies on the dynamic indentation test and characterization have been performed. In this work, a dynamic indentation test technique based on the split Hopkinson pressure bar system is developed, and the corresponding “three-wave method” is proposed to effectively acquire the time-resolved dynamic indentation load and depth. Systematic indentation tests under different loading rates and indenter cone angles are conducted on typical metal materials such as Cu, α-Fe, and α-Ti. Based on the dynamic indentation contact stiffness analysis and indentation theory the indentation hardness under different loading conditions are determined. A procedure for plastic parameter inversion of metal materials, including strain hardening and strain rate strengthening terms based on dynamic indentation, is provided. The effectiveness is verified by the traditional compression test results, providing a new method for characterizing the dynamic mechanical properties of metal materials.

Surface nanoprecipitation induced by severe plastic deformation in the Fe49.3Co23Ni23C0.85Mn1Si2.85 biphasic multicomponent alloy

Precipitation strengthening plays a vital role in enhancing the mechanical properties of metallic materials, typically achieved through heat treatment. However, deformation-induced precipitation (DIP) in multicomponent alloys (MAs) without the assistance of annealing is rarely reported, owing to their inherent high entropy and sluggish diffusion effects. This work reveals the significant formation of nanoscale and microscale precipitates in the dual-phase Fe49.3Co23Ni23C0.85Mn1Si2.85 MA triggered by surface severe plastic deformation (SSPD) through industrial shot blasting. The SSPD process leads to the formation of ultrafine gradient structures comprising nanocrystalline and submicron-crystalline zones. Submicron SiO2 precipitates emerge at the interfaces of both these zones, while various Mn5Si3 and Si nanoparticles precipitate within the nanocrystalline zone. This phenomenon can be ascribed to the high density of generated substructures, the accelerated diffusion of atoms, and the reduction in solid solubility limits in the SPD-driven non-equilibrium state.

Anisotropy effect on the motion of edge dislocation in body-centered-cubic Fe

The mechanical properties of metallic materials can be dictated by nucleation, multiplication, and motion of dislocations under stress. We employed the molecular dynamics (MD) method to investigate the motion of an 1/2[111](112̄) edge dislocation in body-centered-cubic (BCC) Fe under normal stress on the 112̄ plane. Our MD results confirm that the motion of the edge dislocation can be attributed to the normal stress induced shear stress (NSISS) effect. The magnitude of this effect varies across different cubic metals. Further studies reveal that this effect is limited to the {112} planes and is associated with the disobedience of Schmid’s law in the case of twinning of BCC Fe. To summarize, the NSISS effect may be traced back to the anisotropy of cubic metals and should be considered when the twinning process in anisotropic BCC metals is studied.

(Invited) Mechanical Property Design of Multilayered Ti/Au Microcomponents by Electrodeposition Toward High-Sensitive MEMS Accelerometers

Recently, MEMS accelerometers employing Au components prepared by electrodeposition are reported to have a small size whiling retaining a high sensitivity [1], which is mainly contribute by Au’s high mass density, as shown in Fig. 1. Detections of body tremors and muscular sounds are realized using this highly sensitive MEMS accelerometer [2]. However, low mechanical strength of Au, when compared to Si-based materials commonly used in conventional MEMS accelerometers, leads to insufficient structure stability for the long-term use of the device. To enhance the mechanical strength of Au-based materials, several approaches have been reported; for example, multi-layered metal technology [3], and alloying Au with Cu [4]. On the other hand, effects of such approaches on the long-term structure stability of the Au-based materials with dimensions in micro-scale remain uncleared. Considering the relationship between mechanical properties of metallic materials and size of the specimens evaluated, evaluation of the long-term structure stability of Au-based materials in micro-scare is essential for commercial uses of the Au-based MEMS device.Cantilever-like structures are commonly used in movable components in MEMS devices [1, 3]. Repeatedly electrodeposition of gold following by deposition of a material with a high mechanical strength to realize a multi-layered structure is an effective strategy to enhance the structural stability [5]. From the Euler-Bernoulli beam theory, the structural stability of a cantilever-like structure is improved by using materials having high Young's modulus (as noted E). Although, the E is an intrinsic property of materials, which should be constant as the specimen size changes, but the E of small-sized specimens is reported to differ as the size changes. The E of a small-sized specimen with a specific geometry is called the effective Young’s modulus (E eff). The E eff of a micro-cantilever could be determined from the resonance frequency of the micro-cantilever, and the resonance frequency could be measured by a laser doppler vibrometer [4].In this report, various Ti/Au multi-layered structures, as shown in Fig. 2, were prepared. Firstly, the E eff of complex three dimensional (3D) multi-layered Ti/Au structures was determined from the resonance frequency obtained with a laser doppler vibrometer, as shown in Fig. 3. Next, we studied the effects of these various Ti/Au multi-layered structures on the long-term structure stability by vibration tests. Lastly, we discuss the relationship between the Ti/Au multi-layered structures with characteristic E eff values and long-term structure stability. The discussion could contribute to the material design for highly sensitive and stable MEMS accelerometers.Reference: Yamane, et al., Appl. Phys. Lett., 104, 074102 (2014).Onishi, et al., Jpn. J.Appl.Phys., 61, SD1028 (2022)Machida, et al., ECS Trans., 61, 21 (2014).Nitta, et al., J.Electrochem.Soc., 167, 082503 (2020)Teranishi et al., Microelectro. Eng. 187–188 , 105–109 (2018) Figure 1

Role of and dislocations on the room-temperature grain boundary migration in a deformed Mg alloy

During deformation, dislocation movements at grain boundaries (GBs) directly affect GB plastic behaviors, thus affecting the mechanical properties of metal materials. As common defects in deformed Mg alloys, the specific role of <a> and <c+a> dislocations on room-temperature GB migration is still unclear. This work systematically investigates and answers this scientific question via experimental observations and atomic simulations. High-density serrated GBs of the AZ80 Mg alloy are achieved by multi-axial compression at room temperature. At the atomic scale, the overall slip of interfacial <a> dislocations leads to GB migration, while the GB can remain flat. Different local migration rates caused by slip and interlock of adjacent <a> and <c+a> dislocations result in GB steps, thus forming the serrated GB as the deformation proceeds. The basal-pyramidal lock at the GB prevents the continuous migration of the local GB. A new basal-pyramidal lock model at the GB is established to give a criterion for stable interlock of partial <a> and <c+a> dislocations. The experimental results and the atomic simulations show good agreement at the atomic scale and atomic simulations can explain the GB structure changes observed in the experiments. This work contributes to understanding the GB migration mechanisms of Mg alloys, which helps design deformed Mg alloys through GB engineering.

Nickel content-dependent microstructure and mechanical properties of TiZrNbHfNi high entropy alloy thin films

Alloying is known as an effective strategy to improve the mechanical properties of metallic materials. Here we show that the microstructure and mechanical behavior of a TiZrNbHf1.6 high entropy alloy film can be highly tuned by Ni addition. The newly designed TiZrNbHf1.6Nix (x = 0, 0.4, 1.2, 1.8, 2.5, 3.0, 4.6) alloy films are synthesized by co-sputtering Ti, Zr, Nb, Hf and Ni elemental targets. The microstructure and mechanical behavior of the alloy films are investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and nano/micro-indentations. The microstructural analysis indicates that the TiZrNbHf1.6 film has a single body-centered cubic with columnar-nanograined structure. As Ni content increases to 0.4 or above, the films show a complete amorphous structure. Our theoretical analysis shows that the transition from the crystalline to the amorphous structure can be attributed to the large atomic radius difference and the change of the thermodynamic parameters (e.g., mixing entropy and mixing enthalpy) due to the Ni addition. Compared to the TiZrNbHf1.6 film with a hardness of 4.8 GPa, a hardness increase of 8–35% is achieved in the Ni-doped alloy films (5.2–6.5 GPa) as measured by nanoindentation. The elevated hardness may be attributed to the severe lattice distortion and the amorphous structure induced by the Ni addition. Furthermore, microindentation reveals a diversity of deformation behavior in those films with different Ni content. A homogeneous deformation (slight plastic pileup) occurred in the films with Ni content of 1.2 and 4.6, which is close to the deformation behavior of the crystal TiZrNbHf1.6 film. While the film with a Ni content of 1.8 exhibits a catastrophic cracking deformation. Finally, multiple shear banding dominates the deformation of these films with Ni content of 0.4, 2.5 and 3.0. Our findings demonstrate that ultrastrong and highly deformable amorphous high entropy alloy thin films can be developed by appropriate element addition, making them promising materials for corrosion and wear-resistant coatings.

Effect of compositional heterogeneity on the mechanical properties of a single-phase Cu-9Al alloy with different grain sizes

Recent investigations have indicated that compositional heterogeneity, which is compositional undulation of alloying elements in single-phase solid solutions, can enhance the strength without sacrificing ductility, similar to cluster strengthening, of single-crystal nano-pillars and bulk nanocrystalline metallic materials. However, the impact of compositional heterogeneity on the mechanical properties of coarse-grained metallic materials is not yet fully understood. In this study, we examine the influence of compositional heterogeneity on the tensile mechanical properties of a Cu-9Al (at.%) alloy with a coarse-grained structure fabricated using wire arc additive manufacturing and with an ultrafine-grained structure after further processing. Our results demonstrate that the effects of compositional heterogeneity depend significantly on the grain size. Specifically, in ultrafine-grained samples, there is a remarkable improvement in strength with only a slight reduction in ductility. However, as grain size increases, the strengthening effect of compositional heterogeneity diminishes, resulting in softening with a significant loss of ductility. These phenomena can be attributed to the behaviour of dislocations in the materials. Overall, this study highlights the importance of understanding the relationship between compositional heterogeneity, grain size, and mechanical properties in metallic materials, which can inform the design of new materials with improved strength and ductility.

Improvement of Tensile Strength of Friction Stir Processed AA6086/Tic Surface Composite

: Friction stir processing (FSP) is a new solid state processing technique that can eliminate casting defects and refine micro structures, enhances mechanical properties of metallic materials. FSP can also produce fine grained structure and can able to fabricate the surface composite. The Aluminum alloy (Al–Mg–Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to-weight ratio and good corrosion resistance especially in aerospace and automotive industry.&#x0D; In this work , The concept of friction stir processing was utilized to successfully disperse the titanium carbide particles of 5 µm on to the surface of AA6086.The Taguchi Design Of Experiments (DOE) was applied to determine the most important factors which influences the ultimate tensile strength of AA6086/TiC surface composites produced by friction stir processing. An L9 orthogonal array, Signal to Noise ratio, Analysis of Variance (ANOVA) were applied to study the performance characteristics. The high value of S/N ratio indicated that the speed is the most influential parameter and the ANOVA results showed that rotational speed is the most influential parameter. Based on experimentation and statistical analysis, it is found that the UTS is higher with higher rotational speeds and is better with lower transverse feeds.

Improvement of Tensile Strength of Friction Stir Processed AA6086/Tic Surface Composite

Friction stir processing (FSP) is a new solid state processing technique that can eliminate casting defects and refine micro structures, enhances mechanical properties of metallic materials. FSP can also produce fine grained structure and can able to fabricate the surface composite. The Aluminum alloy (Al–Mg–Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to-weight ratio and good corrosion resistance especially in aerospace and automotive industry.&#x0D; In this work , The concept of friction stir processing was utilized to successfully disperse the titanium carbide particles of 5 µm on to the surface of AA6086.The Taguchi Design Of Experiments (DOE) was applied to determine the most important factors which influences the ultimate tensile strength of AA6086/TiC surface composites produced by friction stir processing. An L9 orthogonal array, Signal to Noise ratio, Analysis of Variance (ANOVA) were applied to study the performance characteristics. The high value of S/N ratio indicated that the speed is the most influential parameter and the ANOVA results showed that rotational speed is the most influential parameter. Based on experimentation and statistical analysis, it is found that the UTS is higher with higher rotational speeds and is better with lower transverse feeds.

Effect of gradient microstructure on the bendability of AZ31 alloy sheet

Extensive researches have elucidated the pronounced benefits of gradient microstructures for the mechanical properties of metallic materials. However, the ramifications of gradient microstructures on formability, particularly regarding their effects on bendability, remain inadequately understood. In this work, the effects of gradient microstructure on the bendability of AZ31 Mg alloy sheet are systematically investigated by comparing the microstructure evolution and strain distribution in the sheets with uniform microstructure (grain size = 12.8 µm and 91.3 µm) and gradient microstructure (grain size = 11.5–75.4 µm). The results show that the bendability of the sheet with gradient microstructure is significantly improved when the fine grains (FGs) are placed at the outer side (TBE-FG sample) and the bendability is increased by 93.1% compared to the sample with fine and uniform microstructure (CE-FG sample). With coarse grains (CGs) placed at the inner side, the strain at the compressive region of the TBE-FG sample is higher than its counterparts, while the tensile strain at the extended region is lowest among the four samples. Quasi-in-situ bending experiments reveal that the CGs at the inner side of the TBE-FG sample undergo more twinning. Moreover, the increment of residual dislocation density at the outer side of the TBE-FG sample is lower than those of other samples, which extends the bending potential. This work provides a novel perspective to improve the bendability of the Mg alloy sheet.

Grain boundary alloying segregation to resist hydrogen embrittlement in BCC-Fe steels: Atomistic insights into solute-hydrogen interactions

Grain boundary (GB) segregation of alloying elements is widely recognized to influence the mechanical properties of metallic materials. However, the rational utilization of GBs' chemical heterogeneity to mitigate hydrogen embrittlement (HE) remains challenging. Here, we employ comprehensive first-principles calculations to investigate solute-hydrogen interactions across five distinct GBs. The calculations provide fundamental insights into H concentration, transport, and induced decohesion at BCC-Fe Σ5(013)[100] GB with alloying segregations including W, Mo, Nb, and Mn, emphasizing the crucial importance of hydrogen adsorption energies. Through statistically identifying the effective descriptors derived from complex atomic environments of various GBs, we elucidate solute-hydrogen interaction mechanisms at GBs from broadly applicable solute valence and electronegativity factors. The analysis highlights the vital role of concurrently controlling alloying segregation tendency, GB separation work, and local H solubilities, thereby comprehending GB engineering strategies and facilitating design of high-performance alloys with GBs resistant to HE.

Dynamic yielding and plastic flow behavior of Ti-6Al-4V under complex loading

The mechanical properties of metallic materials under complex loading at high strain rates are very important for material processing and engineering design. In this paper, a newly developed electromagnetic Hopkinson bar system is used to conduct dynamic experiments on Ti-6Al-4V titanium alloy under tension/compression-torsion loading conditions. The dynamic plastic behavior of the alloy, subject to complex stress states, was investigated at different loading rates under tension–torsion and compression-torsion conditions. A dynamic asymmetry yield criterion (DAYC) and loading surface (DALS) with different loading paths were proposed. The coupling effects of strain rate and stress state were considered in the yield and hardening functions. The results reveal non-uniformity in the initial yield surface and the expansion of loading surfaces at different stress states under high strain rates. Through comparison with experimental results, the reliability and accuracy of the proposed yield criterion and loading surface were validated. At last, a study on the direction of plastic flow was conducted, which demonstrated that the associated flow rule was basically satisfied.

Strengthening mechanisms of a heterostructured pure aluminum with extraordinary mechanical properties

To achieve superior mechanical properties in metallic materials, one promising way is to make them into heterogeneous structures (HS). In this work, a novel HS including grain size and dislocation density is developed in commercial pure aluminum through cold-rolling and subsequent partial annealing processes. Tensile tests show that the HS specimen, annealed at 150 °C for 2 min with ~31.1% recrystallized grains, have a high yield strength of ~121 MPa and a good uniform elongation of ~8.5%. The yield strength increases by 10% and the ductility increases by 7 times compared with the as-rolled specimen, respectively. Detailed microstructure characterizations confirm that a significant strain gradient was generated near the interface between the hard zone and soft zone, in which the slip and plugging of geometrically necessary dislocations act as an important role in the abnormal hardening and strengthening phenomena of the HS specimen. To quantify the specific contribution of each strengthening mechanism, we compare the experimental measurements with the theoretical calculations and confirm that the multiple deformation modes are activated by the deformation stress. The hetero-deformation-induced hardening and strengthening effects are responsible for the superior mechanical properties of the heterostructured pure aluminum.

Mechanical Properties of Metallic Materials Processed by Surface Severe Plastic Deformation

This paper gives an overview about some mechanical properties of materials processed by surface severe plastic deformation (SSPD) techniques. SSPD processed materials are classified in terms of their characteristics, and some main generated parameters that determine the output properties of materials are presented. The influences of SSPD on mechanical properties of materials are then reviewed. Furthermore, the roles played by some important parameters such as gradient microstructure, nanostructured layer, compressive residual stress (CRS) and surface integrity are highlighted by discussing their contributions to the mechanical properties of materials. Finally, some conclusions are drawn and possible prospects for future research are underlined.