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Additive manufacturing (AM) of biomedical alloys such as Co-Cr-Mo alloys holds immense potential for fabricating implants with complex geometry and tailored to meet patient-specific needs. However, layer-by-layer fabrication in AM processes results in undesired anisotropy due to the solidification texture and grain morphology. The present study aimed to investigate the effect of build orientation on the mechanical properties and functional performance, including tribocorrosion behavior and cytocompatibility of an orthopedic Co-28Cr-6Mo alloy manufactured by selective laser melting. Although the fabricated alloy showed weak crystallographic texture due to the rotational scanning strategy, significant anisotropy was found in the tensile properties due to the grain size and morphology. The presence of larger, elongated grains along the build direction as compared to smaller, equiaxed grains perpendicular to the build direction imparted the observed tensile anisotropy. Quantitative analysis based on current models for strengthening mechanisms is insufficient to explain the observed anisotropy, which is ascribed to the possible role of the cellular dendrites and stacking fault strengthening in Co-Cr alloys. Unlike the electrochemical behavior, which was largely independent of the build orientation, the bio-tribocorrosion studies revealed an anisotropic wear rate under fretting conditions. Osteoblast attachment and proliferation were found to be higher on the plane perpendicular to the build direction, owing to the differences in grain size. This work provides novel insights into the role of the manufacturing parameters in a selective-laser-melted Co-Cr alloy and its potential application in engineering load-bearing orthopedic implants.

AM technologies allow for the fabrication of complicated geometric components at reduced costs and with better functionality. Aside from design complexity, regulating desired textures during AM processes can provide a substantial advantage. Microstructures are typically columnar along the build direction and equiaxed across the build plane. Columnar grain structures are characterized by a high crystallographic texture and mechanical anisotropy. The crystallographic texture is a key material parameter that has a significant impact on a product's functionality. Mechanical anisotropies result from preferred crystallographic orientations. Additive manufacturing processes acquire crystallographic texture primarily through solidification, which is influenced by local heat flow directions and competing grain growth in the chosen crystallographic direction. This paper provides a comprehensive explanation of the foundations of solidification structure and texture as they pertain to additive manufacturing in some of the most widely researched structural metals, particularly steels, nickel-base superalloys, and titanium alloys.

Third generation γ-titanium aluminides with nominal compositions Ti–45Al–5Nb–0.2B–0.2C and Ti–45Al–10Nb–0.2B–0.2C were investigated to identify the phase transformation and their morphological stability with temperature. Electron microscopy and differential scanning calorimetry were employed for the characterization of phases and for recording the corresponding transformations, respectively. It has been inferred that the order–disorder transformation temperatures α2 → α increased with increasing Niobium (Nb), while the α-transus temperature decreases. The stability of the microstructure for both alloys with temperature were also investigated. Mass change measured for the heating rates 20 °C s−1 and 30 °C s−1 reveals that the alloy Ti–45Al–10Nb–0.2–0.2C shows stability up to 1100 °C, and the alloy Ti–45Al–5Nb–0.2B–0.2C is stable up to 900 °C. The orientation relationship between the phases indicates that with the change in shape of the α phase from lamellar to equiaxed, it deviates from the Blackburn orientation relationship.

The evolution of microstructure and texture during selective laser melting (SLM) of silver alloy—sterling silver 925 (AM Ag925) has been investigated and analyzed vis-a-vis cast sterling silver (AC Ag925). The microstructure of AM Ag925 was characterized by a single-phase silver-rich face-centered cubic solid solution with dendritic morphology, along with some locally distributed micro-segregated copper–germanium (Cu–Ge)-rich regions. Each adjacent dendritic feature consists of Ag–Cu-rich and Ag–Ge-rich regions and appears as alternate dark and bright regions. On the other hand, the as-cast AC Ag925 microstructure comprises Ag and Cu phases. Specific heat treatment was employed, which led to an equiaxed microstructure in AM Ag925 with Cu distributing along grain boundaries while the microstructure of AC Ag925 had Cu precipitates inside the matrix. Bulk texture studies revealed that the solidified textures were very weak for AM Ag925, and a random texture is observed. On the other hand, for the AC Ag925 specimens, a typical fiber texture is observed. Both AC Ag925 and AM Ag925 showed significant deviation from $$\left\langle {100} \right\rangle$$ solidification texture and influences the mechanical properties.

An anomalous deformation texture evolution has been observed in high-stacking-fault-energy pure platinum during cold rolling. A maximum of 98% thickness reduction, equivalent to a true strain of 3....

Additive manufacturing (AM) has emerged as an alternative tool to overcome the challenges in conventionally processed metallic components. It is gaining wide acceptability because of the superior properties of the manufactured components compared to their wrought processed counterparts. Among the available AM processed materials, austenitic stainless steel 316L is widely explored wherein an excellent strength-ductility trade-off has been reported. However, the mechanisms underlying fracture toughness of AM stainless steel 316L vis-a-vis wrought processed stainless steel 316L material are not yet explored. The present investigation is aimed at examining the mechanisms accountable for the fracture toughness of AM processed stainless steel 316L. The specimens are produced by two different AM techniques namely, selective laser melting (SLM) and wire arc additive manufacturing (WAAM). A wrought processed stainless steel 316L was used as a control material for comparison. Three-point bending tests were carried out on fatigue pre-cracked single edge notched specimens and crack initiation fracture toughness was evaluated. Digital image correlation was used for strain analysis and to monitor crack propagation. The SLM manufactured sample has shown higher fracture toughness whereas WAAM has exhibited nearly the same fracture toughness when compared to the wrought processed stainless steel 316L sample. Microstructure of fractured samples consists of a significantly higher twin density and a higher propensity of dislocation slip was observed in the SLM sample than the other two. It has been argued that a very fine cellular structure, minimized process-induced defects, enhanced twin density led to promising toughness in the SLM processed stainless steel 316L.

Metal additive manufacturing processes offer unique opportunities for the biomedical industry owing to their ability to produce custom-designed implants with near-net shape and intricate geometry. Co–Cr alloys are among the most popular metallic biomaterials due to their excellent resistance to both corrosion and wear. Several studies have been reported in recent years on studying the processing-structure–property relationships in additively manufactured Co–Cr alloys. However, there is a significant gap in knowledge of critical issues such as the microstructural features and properties of additively manufactured parts as well as the role of the processing parameters and post-manufacturing treatments. The performance of the additively manufactured Co–Cr alloys for biomedical applications such as fatigue, wear, corrosion, and the biological response is poorly characterized as yet. This article presents an overview of the existing literature available on additively manufactured Co–Cr alloys and identifies challenges and opportunities for their use in biomedical implants.

The alloy Ti6Al7Nb with the in situ reinforcement of TiB has been processed by selective laser melting (SLM). Premixed Ti6Al7Nb-xTiB2 powders were used for the powder bed. The microstructure of the Ti6Al7Nb alloy was characterized by martensite (αʹ), while the addition of TiB2 led to a bimodal microstructure with refined features as a result of in situ formation of fine TiB phase. A prismatic ││BD fiber texture was evident in all samples, though the texture formation was found to be affected by the change in the phase transformation pathway due to the formation of TiB. Higher hardness and yield strength (YS) in the composites as compared to the base material are attained. The examination of corrosion response revealed a lower corrosion current (Icorr) value for all the specimens in simulated body fluid (SBF) in comparison to Ti6Al4V alloy. The improved mechanical behavior and better corrosion resistance indicate the potential of SLM-processed Ti6Al7Nb/TiB composite as a suitable replacement for Ti6Al4V alloys for bio-implants.

The role of shear strain and deformation temperature on the microstructure and texture evolution in commercially pure (CP) titanium was investigated in the present study. CP titanium samples were s...

This study investigates heterogeneity in the deformation of an annealed sheet of commercially pure titanium (cp-Ti), its variation with loading direction and its influence on dwell fatigue response...

Thermo-mechanical softening forms the basis for hot working of metallic materials. In materials with hierarchical microstructures such as martensite, softening processes can be mediated or restricted by interfaces. In the present study, the operation of three distinct softening mechanisms in P91 martensitic steel during thermo-mechanical processing (TMP) has been investigated. The softening in the present case is found to arise from the interplay between microstructural strain, texture, and phase transformation. Further, softening characteristics vary with the TMP parameters. The manifestation of softening has been explored at the macroscopic, mesoscopic, and microscopic length scales. It has been found that each softening mechanism is differently mediated by the interfaces and is governed by local crystallographic orientation. Thermo-mechanical softening of martensite proceeds through orientation-dependent dynamic recrystallization. The role of specific interfaces in impeding this mechanism has been highlighted. In contrast, TMP of austenite proceeds through interface-mediated softening, combining the phenomena of recrystallization and phase transformation.

Microstructure evolution and texture development during cold rolling of a Ti15333 alloy were systematically investigated in the present work. Texture was simulated using mean-field [Visco-Plastic Self-Consistent (VPSC) and Taylor] models. Evolution of crystallographic texture was also simulated using the Visco-Plastic Fast Fourier Transform (VPFFT) model. The as-received samples (in the hot-forged and hot-rolled condition) were cold rolled unidirectionally up to 20, 40, 60 and 80 pct thickness reductions. Increase in the cold-rolling reduction resulted in changes in the crystallographic texture as well as grain morphology. The initial hot-rolled sample consisted of in-grain shear bands that were aligned approximately ± 35 to 40 ° with respect to the sample rolling direction. Shear band density gradually increased with the increase in cold-rolling reduction, and these bands usually represent narrow zones of intense strain. α (RD//〈110〉) and γ (ND//〈111〉) fibers were observed in all the cold-rolled samples. The volume fraction of both these fibers was found to be highest for the 80 pct deformed sample. For mean-field simulations, the normalized difference of the texture index (normalized TIdiff) was found to be a good criterion to represent the match between the simulated and experimental texture. The affine model (VPSC) was found to give a good match with the experimental texture compared to the Taylor models. The γ-fiber and α-fiber were always overestimated in mean-field VPSC simulations. Extensive shear band formation could be the possible reason for mismatch between the simulated and experimental texture. For VPFFT simulations, the general texture evolution involved the intensification of the γ-fiber and α-fiber texture. Simulated texture was reasonably well predicted quantitatively with VPFFT, analyzed based on the volume fraction of the different texture fibers/components.

Hot deformation and softening response for the titanium aluminide Ti–48Al–2V–0.2B has been investigated. The deformation response to softening mechanisms has been examined. Deformation experiments were carried out in the strain rate range 0.01–10 s−1 keeping the temperature constant at 1200 °C and in the temperature range 1000–1200 °C at the strain rate 1 s−1. With an increase in strain rate, the microstructural changes associated with the softening mechanism include breaking of the lamellae, spheroidization of the broken laths and dynamic recrystallization. For the strain rate 1 s−1, deformation in the (α2 +γ) phase field leads to fine recrystallized grains, remnant lamellae and cavitation along the grain boundaries (for temperatures 1000 and 1100 °C). Deformation in the (α +γ) phase field leads to dynamic recrystallization at the shear bands, within the lamellae, breaking and rotation of the α phase during the continuous increase in the deformation strain.

Static and dynamic fracture experiments are performed using fatigue pre-cracked three-point bend specimens of a rolled AZ31 Mg alloy on a servo-hydraulic universal testing machine and a Hopkinson bar setup, respectively. The results are interpreted using in-situ optical imaging along with digital image correlation analysis. Microstructural analysis reveals that the fracture mechanism changes from twin-induced quasi-brittle cracking for static loading to micro-void growth and coalescence under dynamic loading accompanied by decrease in tensile twinning near the tip with loading rate. By contrast, the density of twins near the far-edge of the ligament and associated texture change enhance strongly with loading rate. The fracture toughness increases dramatically at high loading rates which is attributed to enhanced work of separation and dissipation in the background plastic zone.

In the present investigation, the evolution of texture and microstructure during incremental sheet forming was investigated. Hot-rolled sheets of commercially pure titanium were subjected to single-point incremental forming to obtain truncated pyramid geometries. It was observed from texture measurements that there was splitting of basal poles along the transverse direction. Moreover, a significant number of twins was observed in the deformed microstructure with the fraction of extension twins being highest compared to other variants. The crossing of deformation twins, formation of twin lamellar structure and formation of secondary extension twins within primary contraction twins were additionally observed. The state of deformation in the pyramid walls was analyzed via finite element method which in turn was used as input for carrying out crystallographic texture simulations via visco-plastic self-consistent simulations. It was observed that the state of deformation in the wall regions is plain strain compression plus through-thickness shear.

The thermoelectric efficiency of skutterudite materials can be improved by lowering the lattice thermal conductivity via the uniform dispersion of a nanosized second phase in the matrix of filled C...

Mixed-mode (I/II) fracture experiments on rolled AZ31 Mg alloy are conducted using notched four point bend specimens along with in-situ imaging. Digital Image Correlation (DIC) technique is used to analyze the images and map out the deformation and strain fields. With increase in mode II component of loading, a monotonic reduction in the notched fracture toughness (Jc) is observed. Fractographs reveal that the fracture mechanism transitions first from (ductile) micro-void growth and coalescence to twin induced quasi-brittle failure and then to shear cracking as the loading changes from mode I to II. Detailed optical micrographs and EBSD maps show profuse tensile twinning in the ligament, especially near the far-edge of the specimen leading to pronounced texture changes. However, the micro void size near the notch tip as well as the twin density in the ligament reduce with higher mode II component. The pronounced drop in fracture toughness and the changes in the associated mechanism with increase in mode-mixity are rationalized from the combined effects of hydrostatic stress, plastic strain localization and tensile twinning.

In the present study, the Fe-Al-based compositions developed as low-density steel are subjected to addition of Cr and Mn to increase the elastic modulus. In this regard, Fe-3.7Al-3.1Mn and Fe-6.5Al-6.3Cr steels are produced via melting and casting. The steels are cold-rolled to 98% thickness reduction followed by subsequent annealing at 750 °C. A detailed characterization based on x-ray diffraction and electron back-scattering diffraction shows the stabilization of ferrite phase upon the addition of Cr and Mn with a further reduction in density. The expansion of the lattice is observed after ternary alloying additions. The increase in the yield stress and ultimate tensile strength is noticed upon ternary alloying additions. The Cr and Mn addition also led to an increase in the elastic modulus compared to binary Fe-Al low-density steels.

In this investigation, the superalloy IN718 has been prepared by additive manufacturing (AM) following a selective laser melting technique, and the post-AM heat treatments have been optimized. The microstructure of additively manufactured (AM) IN718 is characterized by the presence of dendritic and cellular features with large spatial heterogeneity along and across the build plane. Along the build direction, the fiber texture dominates. Heat treatment involving two-step solution treatment, and subsequently, two-step aging treatment was specifically designed to facilitate the precipitation of d phase at the grain boundaries to make the material resistant to grain boundary sliding (GBS). The AM IN718 showed dynamic strain aging (DSA) at three different temperatures, while the critical strain for the onset of serration was extended to a higher value after the heat treatment.

Ti-Nb-based low modulus metastable β-titanium alloys are popular choice for orthopedic implant materials. The performance of these materials could be affected by variation in crystallographic texture developed during processing. In the present study, texture evolution during unidirectional rolling and multi-step cross-rolling of the alloys Ti-34Nb-2Ta-3Zr-0.5O (TNTZO) and Ti-34Nb-2Ta-0.5O (TNTO) (in wt pct) has been studied. In both the alloys, the rolling texture is characterized by the absence of RD∥〈110〉 fiber, and cross-rolling leads to a stronger texture than unidirectional rolling. However, the prominent texture components in the cross-rolled condition are different for the two alloys. The TNTZO alloy shows the formation of a strong γ-fiber (ND∥〈111〉) along with {001}〈110〉 components while in TNTO, the texture is dominated by strong {001}〈110〉 component. These experimental results have been analyzed by simulations using viscoplastic self-consistent model and further validated by microstructural analysis using electron back scattered diffraction (EBSD). The deformation texture evolution has been attributed to a predominantly $$ \left\{ {11\overline{2} } \right\}\left\langle {111} \right\rangle $$ slip. The simulated texture of Ti-34Nb-2Ta-0.5O alloy shows a minor deviation from the experimental texture, which can be related to the reduced stability of this alloy due to the absence of Zr.

The formation of shear bands during hot deformation of a two-phase (α2 + γ) titanium aluminide and its consequences on dynamics softening has been investigated. The starting material consists of a colony of lamellar grains along with the segregated vanadium and niobium which was subjected to hot deformation in the temperature range 1000–1175 °C at the strain rate 10 s−1. Microstructures of the deformed samples indicate that, with increase in the deformation temperature, the orientation of shear bands changes. Moreover, the extent of dynamic recrystallization also increases with deformation temperature. The softening behaviour and crystallographic orientation change within lamellae during hot deformation have been explored. The nucleation of newly recrystallized grains has been observed at twin–parent grain boundary and within the twined γ phase. Lamellae of the γ and α2 phase have been also observed to be twisted and tilted, leading to the band formations under the load, whose mechanisms have also been explored in the present study.

This article presents the texture development of magnesium AZ31 alloy in the accumulative roll bonded (ARB) AZ31/AZ31 multilayer and AZ31/AA5086 laminate composite. The comparative study demonstrates that the texture evolution in AZ31 in a multilayer system is strongly influenced by the interfaces. A typical basal texture of AZ31 has been observed in AZ31/AZ31 multilayer with texture intensity increased with the rolling deformation. Presence of AZ31/AA5086 interface in the laminate composite leads to a tilted basal texture along the rolling direction (RD) in AZ31 alloy. The texture intensity of composite increased initially with rolling reduction and weakened at the higher rolling strain. Weakening of texture in AZ31 during the laminate processing at higher strain has been attributed to the development of wavy interfaces in AZ31/AA5086 laminate.

The evolution of deformation texture and microstructure in commercially pure Al (cp-Al) and two Al–Mg alloys (Al–4Mg and Al–6Mg) during cold rolling to a very large strain (true strain et ≈ 3.9) w...

In this study, mechanical properties and microstructural investigation of Ti64 at high strain rate are studied using a split-Hopkinson pressure bar method under compression for temperatures up to 800 °C. Flow softening in the mechanical response of material to such loading conditions hints at instability in compression, which increases with an increase in temperature. Microstructural characterization of the deformed material is characterized using the electron-backscattered diffraction technique. It reveals the presence of instabilities in Ti64 in the form of a fine network of shear bands. The shear band width grows with an increase in temperature along with the area fraction of shear band in the material, displaying its improved capacity to contain microstructural instabilities at higher temperature. After a detailed microstructural investigation, a mechanism for shear band widening is proposed. Based on this mechanism, a path generating nuclei within shear bands is discussed.

Metastable β Ti alloys are widely projected for manufacturing the next generation of biomedical implants. The primary applications of these materials are envisaged in orthopedic, cardiovascular, an...

The effect of ternary zinc (Zn) addition to two-phase magnesium-lithium alloys on the evolution of their microstructure, texture and tensile properties has been investigated. It was observed that the volume fraction of hexagonal close-packed α phase increased with increase in the Zn content. The size of α lamellae reduced with increase in the Zn content. The strength of the alloys in as-cast condition increased with the Zn content due to solid-solution strengthening without compromising the ductility. The tensile properties of these two-phase alloys were found to be strongly dependent on the volume fraction and size of the α phase. Zn addition led to enhancement of the {200} || normal direction (ND) component but weakening of {110} || ND components in the β phase, while increase in the Zn content had a minor effect on the texture of the α phase in cold-rolled condition. The specific strength of the alloy with 2 wt.% Zn was found to be comparable to, while the ductility was higher than, the highest-strength 7075-T73 Al alloy.

This study deals with the evolution of crystallographic texture during secondary processing of aluminium-lithium alloy AA2195 sheets and its effect on the single-point incremental forming (SPIF) process. Significantly different textures were generated in AA2195 alloy sheets by the unidirectional rolling (UDR) and multi-step cross-rolling (MSCR) processes followed by subsequent annealing. The differently textured sheets were then subjected to the SPIF process. For UDR processed sheets, the texture was the strong copper type (Cu-type), whereas in MSCR processed sheets, the texture comprised weak fibres. The UDR samples with strong texture experienced cracking during incremental forming, whereas the MSCR samples could be formed without any cracks. Detailed analyses of the microstructure and texture were performed at various locations on the incrementally formed part to understand the deformation micromechanism at specific locations on the formed component.