Effects of Vanadium Microalloying and Intercritical Annealing on Yield Strength-Ductility Trade-Offs of Medium-Manganese Steels.

In this paper, we investigate the effects of vanadium on the strength and ductility of medium-manganese steels by analyzing the microstructural evolution and strain hardening rates and performing quantitative calculations. Two significantly different contents of vanadium, 0.05 and 0.5 wt.%, were independently added to model steel (0.12C-10Mn) and annealed at different intercritical temperatures. The results show that higher vanadium addition increases the yield strength but decreases the ductility. The maximum yield strength can increase from 849 MPa to 1063 MPa at low temperatures. The model calculations reveal that this is due to a precipitation strengthening increment of up to 148 MPa and a dislocation strengthening increment of 50 MPa caused by a higher quantity of V4C3 precipitates. However, the high density of vanadium carbides leads them to easily segregate at grain boundaries or phase interfaces, which prevents strain from uniformly distributing throughout the phases. This results in stress concentrations which cause a high strain hardening rate in the early stages of loading and a delayed transformation-induced plasticity (TRIP) effect. Additionally, the precipitates decrease the austenite proportion and its carbon concentrations, rendering the TRIP effect unsustainable. Accordingly, the ductility of high vanadium steels is relatively low.

Impact of gadolinium on mechanical properties, corrosion resistance, and biocompatibility of Zn-1Mg-xGd alloys for biodegradable bone-implant applications.

Zinc (Zn) and its alloys are currently regarded as one of the promising families of biodegradable metals for implant applications owing to their suitable biodegradability and biofunctionality. However, the inadequate mechanical properties of as-cast (AC) pure Zn restricted the practical clinical bone-implant applications due to its coarse grain size and hexagon close-packed crystal structure. Here, the impact of gadolinium (Gd) on the mechanical properties, corrosion resistance, hemolysis percentage, anticoagulant activity, and cytotoxicity of AC and hot-rolled (HR) Zn-1Mg-xGd (x = 0.1, 0.2, and 0.3) (wt.%) alloys were investigated for biodegradable bone-implant applications. Tensile testing showed that the HR Zn-1Mg-0.3Gd alloy exhibited the highest tensile strength of 288.1 MPa, tensile yield strength of 250.9 MPa, and elongation of 13.2%. Electrochemical corrosion and immersion tests revealed that the corrosion rates of both AC and HR specimens increased with increasing Gd content in Hanks' solution, and the HR Zn-1Mg-xGd specimens exhibited higher corrosion rates compared to their AC counterparts. The HR Zn-1Mg-xGd specimens showed an increasing hemolysis percentages and decreasing activated partial thromboplastin time (APTT) values with increasing Gd addition. The alloy extracts of HR samples at ≤ 25% concentration exhibited no cytotoxicity toward MG-63 cells, and the HR Zn-1Mg-0.3Gd alloy displayed the highest cell viability among all three alloy extracts at 12.5% concentration. Overall, the HR Zn-1Mg-0.3Gd can be considered a promising biodegradable implant material for bone-implant materials owing to its high mechanical strength and ductility, suitable degradation rate, and satisfying biocompatibility. STATEMENT OF SIGNIFICANCE: In this work, Zn-1Mg-xGd (x = 0.1, 0.2, and 0.3 wt.%) alloys were developed by alloying with gadolinium (Gd) and hot-rolling, and their mechanical properties, corrosion behavior, hemolysis percentage, anticoagulant activity, and cytotoxicity were investigated for biodegradable implant application. Our findings demonstrated that the hot-rolled Zn-1Mg-0.3Gd alloy exhibit the highest ultimate tensile strength of 288.1 MPa, yield strength of 250.9 MPa, and elongation of 13.2%. Hot-rolled Zn-1Mg-xGd alloys show slowly increasing hemolysis percentages and decreasing activated partial thromboplastin time (APTT) values with increasing Gd addition. Extracts of hot-rolled Zn-1Mg-xGd alloys at a concentration of ≤ 25% show no cytotoxicity towards MG-63 cells, and Zn-1Mg-0.3Gd exhibit good cytocompatibility among all three alloys at a concentration of 12.5%.

Compressive and Energy Absorption Properties of Pyramidal Lattice Structures by Various Preparation Methods.

Metallic three-dimensional lattice structures exhibit many favorable mechanical properties including high specific strength, high mechanical efficiency and superior energy absorption capability, being prospective in a variety of engineering fields such as light aerospace and transportation structures as well as impact protection apparatus. In order to further compare the mechanical properties and better understand the energy absorption characteristics of metal lattice structures, enhanced pyramidal lattice structures of three strut materials was prepared by 3D printing combined with investment casting and direct metal additive manufacturing. The compressive behavior and energy absorption property are theoretically analyzed by finite element simulation and verified by experiments. It is shown that the manufacturing method of 3D printing combined with investment casting eliminates stress fluctuations in plateau stages. The relatively ideal structure is given by examination of stress-strain behavior of lattice structures with varied parameters. Moreover, the theoretical equation of compressive strength is established that can predicts equivalent modulus and absorbed energy of lattice structures.

Compressive Behaviour of Aluminium Pyramidal Lattice Material-Filled Tubes.

This study focuses on the uniaxial compressive behaviour of thin-walled Al alloy tubes filled with pyramidal lattice material. The mechanical properties of an empty tube, Al pyramidal lattice material, and pyramidal lattice material-filled tube were investigated. The results show that the pyramidal lattice material-filled tubes are stronger and provide greater energy absorption on account of the interaction between the pyramidal lattice material and the surrounding tube.

Impact of scandium on mechanical properties, corrosion behavior, friction and wear performance, and cytotoxicity of a ß-type Ti-24Nb-38Zr-2Mo alloy for orthopedic applications.

ß-type titanium (Ti) alloys have been extensively investigated as orthopedic implant materials due to their unique combination of low elastic modulus, high specific strength, corrosion resistance, and biocompatibility. In this study the mechanical properties, corrosion behavior, friction and wear performance, and cytotoxicity of ß-type Ti-24Nb-38Zr-2Mo (TNZM) and Ti-24Nb-38Zr-2Mo-0.1Sc (TNZMS) have been comparatively investigated for orthopedic applications. Cold-rolling (CR) and cold-rolling plus solution-treatment (CR+ST) were performed on the as-cast (AC) alloys and their microstructures and material properties were characterized. The impact of Sc addition on the mechanical and corrosion properties, friction and wear behavior, and in vitro cytocompatibility of the TNZMS alloy was assessed. The CR+ST TNZMS alloy exhibited the best combination of properties among all the alloy samples, with a yield strength of 780 MPa, ultimate strength of 809 MPa, elongation of 19%, Young's modulus of 65.4 GPa, and hardness of 265 HV. Electrochemical testing in Hanks' Solution indicated that the CR+ST TNZMS sample also showed the highest corrosion resistance with a corrosion potential of -0.234 V, corrosion current density of 0.07 µA/cm2, and corrosion rate of 1.2 µm/y. Friction and wear testing revealed that the TNZMS alloy showed higher wear resistance compared to the TNZM alloy and the wear resistance of the different samples was ranked CR > CR+ST > AC. Finally, both the CR+ST TNZM and TNZMS showed no-cytotoxicity towards MG-63 cells and the TNZMS exhibited slightly higher cytocompatibility than the TNZM alloy. STATEMENT OF SIGNIFICANCE: This work reports the ß-type Ti-24Nb-38Zr-2Mo (TNZM) and Ti-24Nb-38Zr-2Mo-0.1Sc (TNZMS) alloys fabricated by as-cast (AC), cold-rolling (CR), and cold-rolling plus solution-treatment (CR+ST) for potential orthopedic applications. The experimental results showed that the TNZMS alloy exhibited significantly enhanced mechanical, wear, and corrosion properties than those of TNZM alloy; and the CR+ST TNZMS possess a unique combination of the best mechanical and corrosion properties including a yield strength of 780 MPa, ultimate strength of 809 MPa, elongation of 19%, Young's modulus of 65.4 GPa, and corrosion rate of 1.2 µm/y in Hanks' Solution. Both the CR+ST TNZM and TNZMS alloys exhibited non-cytotoxicity towards MG-63 cells and TNZMS showed a higher cytocompatibility than that of TNZM.

Biodegradable Zn-3Mg-0.7Mg2Si composite fabricated by high-pressure solidification for bone implant applications.

Zinc (Zn)-based alloys have been considered potential biodegradable materials for medical applications due to their good biodegradability and biocompatibility. However, the insufficient mechanical properties of pure Zn do not meet the requirements of biodegradable implants. In this study, we have developed a biodegradable Zn-3Mg-0.7Mg2Si composite fabricated by high-pressure solidification. Microstructural characterization revealed that the high-pressure solidified (HPS) composite exhibited uniformly distributed fine MgZn2 granules in an α-Zn matrix. Comprehensive tests indicated that the HPS composite exhibited exceptionally high compression properties including a compressive yield strength of 406.2 MPa, an ultimate compressive strength of 1181.2 MPa, and plastic deformation up to 60% strain without cracking or fracturing. Potentiodynamic polarization tests revealed that the HPS composite showed a corrosion potential of -0.930 V, a corrosion current density of 3.5 µA/cm2, and a corrosion rate of 46.2 µm/y. Immersion tests revealed that the degradation rate of the HPS composite after immersion in Hanks' solution for 1 month and 3 months was 42.8 µm/y and 37.8 µm/y, respectively. Furthermore, an extract of the HPS composite exhibited good cytocompatibility compared with as-cast (AC) pure Zn and an AC composite at a concentration of ≤25%. These results suggest that the HPS Zn-3Mg-0.7Mg2Si composite can be anticipated as a promising biodegradable material for orthopedic applications.

Development of biodegradable Zn-1Mg-0.1RE (RE = Er, Dy, and Ho) alloys for biomedical applications.

Zinc (Zn) and its alloys are receiving great attention as promising biodegradable materials due to their suitable corrosion resistance, good biocompatibility, and highly desirable biofunctionality. Nevertheless, the low mechanical strength of pure Zn impedes its practical clinical application and there have been calls for further research into the Zn alloys and thermomechanical processes to enhance their mechanical properties and biocompatibility. Here, we report on the alloying efficacy of rare earth elements (REEs) including erbium (Er), dysprosium (Dy), and holmium (Ho) on the microstructure, mechanical properties, corrosion and wear behavior, and in vitro biological properties of Zn-1Mg-0.1RE alloys. Microstructural characterization revealed that the addition of 0.1 wt.% REEs had a significant refining effect on the grain size of the α-Zn matrix and the second phases of the alloys. Alloying of the REEs and hot-rolling effectively improved the mechanical properties due to both precipitation strengthening of the second phases of ErZn5, DyZn5, and Ho2Zn17 and grain-refinement strengthening. The highest ultimate tensile strength of 259.4 MPa and yield strength of 234.8 MPa with elongation of 16.8% were achieved in the hot-rolled Zn-1Mg-0.1Ho. Alloying of REEs also improved the wear and corrosion resistance, and slowed down the degradation rate in Hanks' solution. Zn-1Mg-0.1Er showed the highest cytocompatibility of MC3T3-E1 cells cultured directly on the alloy surface and of MG-63 cells cultured in the alloy extract. Zn-1Mg-0.1Dy showed the best anticoagulant property among all the alloys. Overall, these Zn-1Mg-0.1RE (Er, Dy, and Ho) alloys can be considered promising biodegradable metallic materials for orthopedic applications.

Biodegradable ternary Zn-3Ge-0.5X (X=Cu, Mg, and Fe) alloys for orthopedic applications.

Biodegradable zinc (Zn) and its alloys have great potential to be used for orthopedic applications due to their suitable degradation rate and good biocompatibility. However, pure Zn has insufficient mechanical properties, such as low strength and hardness, and poor plasticity, which limits its clinical applications. Here, we report on a new series of ternary Zn-3Ge-0.5X (X=Cu, Mg, and Fe) alloys aiming to achieve good corrosion resistance and biocompatibility, and enhanced mechanical properties via micro-alloying with copper (Cu), magnesium (Mg), and iron (Fe). Hot-rolling has also been applied to the new ternary alloys to further enhance their mechanical properties. Mechanical testing results indicate that both the strength and hardness of hot-rolled Zn-3Ge are significantly improved with micro-alloying of Cu, Mg, and Fe; of which the hot-rolled Zn-3Ge-0.5Mg exhibits the highest ultimate tensile strength of 253.4 MPa and yield strength of 208.5 MPa among all the alloys, 25.9% and 44.7% higher than those of the hot-rolled Zn-3Ge. The degradation rate of the as-cast alloys is lower than that of the hot-rolled alloys in Hanks' solution for 1 month and the hot-rolled Zn-3Ge-0.5Mg alloy exhibits the highest degradation rate of 0.075 mm/y. CCK-8 assay using MG-63 cells indicates that the diluted extracts of Zn-3Ge-0.5X (X=Cu, Mg, and Fe) alloys with concentrations of 12.5% and 25% exhibit no or slight cytotoxicity, and the diluted extracts of Zn-3Ge-0.5Cu alloys show high cell viability of over 100%, showing the best cytocompatibility.

A biodegradable Zn-1Cu-0.1Ti alloy with antibacterial properties for orthopedic applications.

Zinc (Zn) alloys are receiving increasing attention in the field of biodegradable implant materials due to their unique combination of suitable biodegradability and good biological functionalities. However, the currently existing industrial Zn alloys are not necessarily biocompatible, nor sufficiently mechanically strong and wear-resistant. In this study, a Zn-1Cu-0.1Ti alloy is developed with enhanced mechanical strength, corrosion wear property, biocompatibility, and antibacterial ability for biodegradable implant material applications. HR and HR + CR were performed on the as-cast alloy and its microstructure, mechanical properties, frictional and wear behaviors, corrosion resistance, in vitro cytocompatibility, and antibacterial ability were systematically assessed. The microstructures of the Zn-1Cu-0.1Ti alloy after different deformation conditions included a η-Zn phase, a ε-CuZn5 phase, and an intermetallic phase of TiZn16. The HR+CR sample of Zn-1Cu-0.1Ti exhibited a yield strength of 204.2 MPa, an ultimate tensile strength of 249.9 MPa, and an elongation of 75.2%; significantly higher than those of the HR alloy and the AC alloy. The degradation rate in Hanks' solution was 0.029 mm/y for the AC alloy, 0.032 mm/y for the HR+CR alloy, and 0.034 mm/y for the HR alloy. The HR Zn-1Cu-0.1Ti alloy showed the best wear resistance, followed by the AC alloy and the alloy after HR + CR. The extract of the AC Zn-1Cu-0.1Ti alloy showed over 80% cell viability with MC3T3-E1 pre-osteoblast and MG-63 osteosarcoma cells at a concentration of ≤ 25%. The as-cast Zn-1Cu-0.1Ti alloy showed good blood compatibility and antibacterial ability. STATEMENT OF SIGNIFICANCE: This work repots a Zn-1Cu-0.1Ti alloy with enhanced mechanical strength, corrosion wear property, biocompatibility, and antibacterial ability for biodegradable implant applications. Our findings showed that Zn-1Cu-0.1Ti after hot-rolling plus cold-rolling exhibited a yield strength of 204.2 MPa, an ultimate tensile strength of 249.9 MPa, an elongation of 75.2%, and a degradation rate of 0.032 mm/y in Hanks' Solution. The hot-rolled Zn-1Cu-0.1Ti showed the best wear resistance. The extract of the as-cast alloy at a concentration of ≤ 25% showed over 80% cell viability with MC3T3-E1 and MG-63 cells. The Zn-1Cu-0.1Ti alloy showed good hemocompatibility and antibacterial ability.

Degradation behavior, cytotoxicity, hemolysis, and antibacterial properties of electro-deposited Zn-Cu metal foams as potential biodegradable bone implants.

Zinc (Zn) alloys have attracted much attention for biomedical applications due to their biodegradability, biocompatibility, and biological functionalities. Zn alloy foams have high potential to be used as regenerative medical implants by virtue of their porous structure, which allows new bone tissue ingrowth, their low elastic modulus approximating that of natural bone, and their biodegradation, which eliminates the need for follow-up surgery to remove the implants after bone tissue healing. In this context, a biodegradable Zn-Cu foam was fabricated by electrochemical deposition on a foamed Cu template and given a subsequent diffusion heat treatment. The microstructure, mechanical properties, degradation behavior, toxicity, hemolysis percentages, and antibacterial effects of the Zn-Cu foams were assessed for biomedical applications. The Zn-Cu foams exhibited a yield strength of ~12.1 MPa, a plateau strength of 16.8 MPa, and a strain over 50% under compression tests. The corrosion rate of the Zn-Cu foams measured by electrochemical polarization testing was 0.18 mm/y. The Zn-Cu foams showed good blood compatibility with a hemolysis percentage of less than 5%. Cytotoxicity assessment indicated that a 100% concentration of the Zn-Cu foam extract showed clear cytotoxicity against MC3T3-E1 osteoblast cells, but a 12.5% concentration of the extract showed > 90% cell viability. Moreover, the Zn-Cu foams showed good antibacterial effects. STATEMENT OF SIGNIFICANCE: This work reportsa biodegradable Zn-Cu foam with high mechanical strength and ductility, suitable degradation rate, good antibacterial capacity, and good hemolysis property and biocompatibility. The Zn-Cu foam exhibited a yield strength of ~12.1 MPa, a plateau strength of 16.8 MPa, and a strain over 50% under compression tests. The corrosion rate of the Zn-Cu foam measured by electrochemical polarization testing was 0.18 mm/y in Hanks' Solutions. The Zn-Cu foam showed good blood compatibility with a hemolysis percentage of less than 5%. Cytotoxicity assessment indicated that a 12.5% concentration of the foam extract showed > 90% cell viability. Moreover, the Zn-Cu foam showed good antibacterial effects against S. aureus.

Microstructure, mechanical properties, biocompatibility, and in vitro corrosion and degradation behavior of a new Zn-5Ge alloy for biodegradable implant materials.

Zinc (Zn)-based alloys are considered a new class of biodegradable implant materials due to their superior chemical stability and processability compared to biodegradable magnesium (Mg) alloys. In this study, we report a new biodegradable Zn-5Ge alloy with highly desirable mechanical, corrosion, and biological properties. Microstructural characterization revealed the effective grain-refining effect of germanium (Ge) on the Zn alloy. Tensile test results indicated that the hot-rolled Zn-5Ge alloy showed an ultimate tensile strength of 237.0 MPa, a yield strength of 175.1 MPa, and an elongation of 21.6%; while as-cast pure Zn showed an ultimate tensile strength of 33.6 MPa, a yield strength of 29.3 MPa, and an elongation of 1.2%. The corrosion rates measured by potentiodynamic polarization tests in Hank's solution in ascending order are: as-cast Zn-5Ge (0.1272 mm/y) < as-cast pure Zn (0.1567 mm/y) < hot-rolled Zn-5Ge (0.2255 mm/y) < hot-rolled pure Zn (0.3057 mm/y). Immersion tests revealed that the degradation rate of as-cast Zn-5Ge is 0.042 mm/y, less than half of that of hot-rolled pure Zn and ∼62% of that of as-cast pure Zn. Moreover, the Zn-5Ge alloy showed excellent in vitro hemocompatibility and the addition of 5% Ge effectively enhanced the hemocompatibility of pure Zn. CCK-8 assay using murine preosteoblast MC3T3-E1 cells indicated that the diluted extracts at a concentration <12.5% of both the as-cast Zn-5Ge alloy and pure Zn showed grade 0 cytotoxicity; the diluted extracts at the concentrations of 50% and 25% of Zn-5Ge alloy showed a significantly higher cell viability than those of pure Zn. STATEMENT OF SIGNIFICANCE: Zinc (Zn)-based alloys are currently considered a new class of biodegradable implant materials due to their excellent processability. Here, we report a novel Zn-5Ge alloy with highly desirable mechanical, corrosion and biological properties. The tensile test results indicated that the hot-rolled Zn-5Ge alloy showed an ultimate tensile strength of 237.0 MPa, a yield strength of 175.1 MPa and an elongation of 21.6%; while as-cast pure Zn showed an ultimate tensile strength of 33.6 MPa, a yield strength of 29.3 MPa and an elongation of 1.2%. The corrosion rate measured by potentiodynamic polarization tests in Hank's solution in the ascending order is: as-cast Zn-5Ge (0.1272 mm/y) < as-cast pure Zn (0.1567 mm/y) < hot-rolled Zn-5Ge (0.2255 mm/y) < hot-rolled pure Zn (0.3057 mm/y). Immersion tests revealed that the degradation rate of the as-cast Zn-5Ge is 0.042 mm/y, less than half of that of the hot-rolled pure Zn, ∼62% of that of as-cast pure Zn. Moreover, the Zn-5Ge alloy showed excellent in vitro biocompatibility.