“…To reveal the relationship between the deformation parameters and the compression stress, additional dynamic analyses were performed based on the thermal activation‐associated Arrhenius constitutive model 15–17 : where is the strain rate (s −1 ), A is the material constant, f ( σ ) is the stress function, Q is the activation energy (kJ/mol), R is the gas constant (8.31 kJ/mol/K), and T is the absolute temperature (K).…”
Section: Resultsmentioning
confidence: 99%
“…The values of Q are the indicators of the deformation mechanisms associated with the microstructure changes, 5,17,20 which were calculated to be 288 kJ/mol in the α + β phase region and 194 kJ/mol in the β phase region, indicating that the deformation in the α + β phase region shows a greater energy barrier to complete the microstructure change. With respect to the available literature data (Table 2), we found that the Q obtained in the α + β phase region for the present alloy is comparable with those reported by Matsumoto et al 8 for Ti‐5553 (~296 kJ/mol) and by Warchomicka et al 5 for Ti‐55531 (~275 kJ/mol), while it is significantly lower than that reported by Long et al 26 for Ti–6Cr–5Mo–5V–4Al (~316 kJ/mol), probably due to the higher Cr content.…”
Metastable β titanium alloys are promising materials for lightweight and energy‐efficient applications due to their high strength and low density. Thermal–mechanical processing (TMP) is one of the most effective ways to improve the mechanical properties of such alloys. This paper describes a systematic TMP investigation on a new metastable β titanium alloy, including its dynamic mechanical behavior, and microstructure evolution, via isothermal compression tests and electron back‐scattered diffraction characterizations. The results show that the compression stress increases with an increase in the strain rate and a decrease in the temperature. After yielding, the compression stress–strain pattern shows flow‐softening behavior at a low temperature and a high strain rate, while sustaining a steady flow state at a high temperature and a low strain rate. The temperature‐rise effect contributes to a large degree of flow softening at high strain rates. After the correction for temperature rise, the stress–strain constitutive relationships are established, showing that the compression behavior varies in different phase regions. Based on the microstructure characterizations, it is found that the dynamic recovery and dynamic recrystallization dominate the hot deformations in β phase region and at low strain rates, while the deformation band as an additional product is found in α + β phase region and at high strain rates. The results contribute to a better understanding of the TMP for the considered alloy and may also represent a useful database for β‐Ti alloy applications in lightweight mechanical systems.
“…To reveal the relationship between the deformation parameters and the compression stress, additional dynamic analyses were performed based on the thermal activation‐associated Arrhenius constitutive model 15–17 : where is the strain rate (s −1 ), A is the material constant, f ( σ ) is the stress function, Q is the activation energy (kJ/mol), R is the gas constant (8.31 kJ/mol/K), and T is the absolute temperature (K).…”
Section: Resultsmentioning
confidence: 99%
“…The values of Q are the indicators of the deformation mechanisms associated with the microstructure changes, 5,17,20 which were calculated to be 288 kJ/mol in the α + β phase region and 194 kJ/mol in the β phase region, indicating that the deformation in the α + β phase region shows a greater energy barrier to complete the microstructure change. With respect to the available literature data (Table 2), we found that the Q obtained in the α + β phase region for the present alloy is comparable with those reported by Matsumoto et al 8 for Ti‐5553 (~296 kJ/mol) and by Warchomicka et al 5 for Ti‐55531 (~275 kJ/mol), while it is significantly lower than that reported by Long et al 26 for Ti–6Cr–5Mo–5V–4Al (~316 kJ/mol), probably due to the higher Cr content.…”
Metastable β titanium alloys are promising materials for lightweight and energy‐efficient applications due to their high strength and low density. Thermal–mechanical processing (TMP) is one of the most effective ways to improve the mechanical properties of such alloys. This paper describes a systematic TMP investigation on a new metastable β titanium alloy, including its dynamic mechanical behavior, and microstructure evolution, via isothermal compression tests and electron back‐scattered diffraction characterizations. The results show that the compression stress increases with an increase in the strain rate and a decrease in the temperature. After yielding, the compression stress–strain pattern shows flow‐softening behavior at a low temperature and a high strain rate, while sustaining a steady flow state at a high temperature and a low strain rate. The temperature‐rise effect contributes to a large degree of flow softening at high strain rates. After the correction for temperature rise, the stress–strain constitutive relationships are established, showing that the compression behavior varies in different phase regions. Based on the microstructure characterizations, it is found that the dynamic recovery and dynamic recrystallization dominate the hot deformations in β phase region and at low strain rates, while the deformation band as an additional product is found in α + β phase region and at high strain rates. The results contribute to a better understanding of the TMP for the considered alloy and may also represent a useful database for β‐Ti alloy applications in lightweight mechanical systems.
“…Despite being similar particle/substrate material, their work [ 56 ] also suggests that mismatch in salient microstructural features like higher grain boundary area (amorphous phase) in the particle than the substrate slows heat dissipation rate to retain melting in the former than the latter. However, using LIPIT to launch Cu microparticle at 590 m/s, followed by post-mortem characterization of a lift-out lamella [ 140 ], Fig. 12 (f–j) shows no evidence of melting.…”
Section: New Insights On Bonding In Cold Spray Processmentioning
confidence: 99%
“… Figure 12 (a–e) Structural profile of copper particle/substrate system at different times, showing that melting may occur during impact, reprinted with permission from Ref. [ 56 ], copyright 2021 Elsevier; (f, g) SEM micrographs, (h) EBSD inverse pole figure map, (i) kernel average misorientation map showing no evidence of melting for adhered particle, launched at 590 m/s [ 140 ]; (j–l) SEM micrographs of Al microparticle impact-induced craters on a Zn substrate at different impact velocities, showing melting may occur but may not necessarily contribute to bonding, reprinted with permission from Ref. [ 141 ], copyright 2017 American Physical Society.…”
Section: New Insights On Bonding In Cold Spray Processmentioning
Cold spray (CS) processing is a layer-by-layer solid-state deposition process in which particles at a temperature below their melting point are launched to sufficiently high velocities to adhere to a substrate (and previously deposited particles), forming coatings/parts. Despite being in existence for over four decades, particle bonding mechanisms in the CS process are unclear due to the complex particle–particle/carrier gas interactions that obscure assessment. This review evaluates recent findings from single-particle impact approaches that circumvent these complexities and further provide new insights on bonding mechanisms. Theories on the evolution of oxide layer breakup and delamination, adiabatic shear instability, jetting, melting, and interface solid-state amorphization that contributes to bonding are assessed and carefully reviewed. Although there is a unified condition in which bonding sets on, this study shows that no singular theory explains bonding mechanism. Rather, dominant mechanism is a function of the prevailing barriers unique to each impact scenario.
Graphical abstract
Further, it facilitated the study of sizedependent materials behavior [7] and the discovery of novel materials physics, such as dynamic hardness of bulk materials [8,9] or new mechanisms for the dynamic recrystallization in metals. [10,11] LIPIT also has become an established tool for the study of impact processes fundamental to cold spray additive manufacturing [12][13][14][15] or ballistic impact protection, [8,16] and has prospects to unveil mechanisms underlying a broad range of engineering fields, including spacecraft protection against hypervelocity micrometeorites and orbital microdebris, needle-free, ballistic epidermal drug delivery, or prevention of erosion of surfaces by impacting sand particles.
In the first decade of high‐velocity microparticle impact research, hardly any modification of the original experimental setup has been necessary. However, future avenues for the field require advancements of the experimental method to expand both the impact variables that can be quantitatively assessed and the materials and phenomena that can be studied. This work explores new design concepts for the launch pad (the assembly that launches microparticles upon laser ablation) that can address the root causes of many experimental challenges that may limit the technique in the future. Among the design changes contemplated, the substitution of a stiff glass launch layer for the standard elastomeric polymer layer offers a number of improvements. First, it facilitates a reduction of the gap between launch pad and target from hundreds to tens of micrometers and thus unlocks a reproducibility in targeting a specific impact location better than the diameter of the test particle itself (±1.75 µm for SiO2 particles 7.38 µm in diameter). Second, the inert glass surface enables experiments at higher temperatures than previously possible. Finally—as demonstrated by the launch of thin‐film Au disks—a launch pad made of materials standard in microfabrication paves the way to facile microfabrication of advanced impactors.
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