Key Engineering Materials Vol. 508

Abstract: The Texture Developed in High-Temperature β Phase during Friction Stir Welding of Ti-6Al-4V Was Studied. It Was Demonstrated that 0002 and 1120 Pole Figures Calculated from α Phase May Be Employed for Interpretation of Material Flow in the β Phase. Together with Orientation Measurements in Retained β Phase, this Approach Was Shown to Be a Very Simple and Effective for the Texture Analysis. The β Texture Was Found to Be a Mixture of {hkl}<111>-Fiber Texture and D₂(112)[111](Simple-Shear Texture Component.

Abstract: We Successfully Prepared the Rod Glassy Samples of (Fe_1-xCo_x)₇₆Si₉B₁₀P₅ (x = 0~0.4) Bulk Metallic Glass (BMG) with the Diameters up to 3.0 mm by Substituting Fe for a Small Amount of Co Element. A Certain Amount of Co Substitution for Fe Contributes to the Increase of the Glass-Forming Ability (GFA) while Maintaining Good Mechanical Properties (the Fracture Strength up to 3700 MPa). This Co-Added Ferromagnetic Bulk Glassy Alloy System Also Exhibits a Higher Saturation Magnetization of 1.49 T and Lower Coercive Force (H_c, 1.2 A/m). The Fe-Based BMGs with Alloying a Small Amount of Co Element Demonstrate Excellent Combination of High GFA, Good Soft-Magnetic Properties as Well as High Strength.

Abstract: Presently Metallic Rods that Are Used for Spinal Fixtures Cannot Meet the Requirements of both Surgeons and Patients; Surgeons Require the Material to Have a High Young’s Modulus to Suppress Springback during the Operation, whereas Patients Require the Material to Have a Low Young’s Modulus to Prevent the Stress-Shielding Effect. In Order to Develop a Novel Biomedical Titanium Alloy with a Changeable Young’s Modulus for Spinal Fixation Applications via Deformation-Induced ω Phase Transformation. The Effects of Deformation-Induced Phases on the Mechanical Properties of Metastable β-Type Ti-xCr Alloys Were Investigated. The Experimental Results Indicate that the Young’s Moduli, Tensile Strength, and Vickers Hardness of the Ti–(10–12)Cr Alloys Increase Remarkably by Cold Rolling. The Results of the Microstructural Observations of Ti–12Cr Alloys Using a Transmission Electron Microscopy (TEM) Show that Deformation-Induced ω Phase Transformation Occurs during Cold Rolling. Therefore, the Increase in Young’s Modulus of the Alloys Is Attributed to the Deformation-Induced ω Phase, which Is Formed in the Alloy during Cold Rolling at Room Temperature.

Abstract: To Understand the Mechanisms of Accelerated Dynamic Recrystallization Behavior during the Warm Deformation of Martensites, the Tempered Lath Martensite of 0.4C Steel (Fe-0.399%C-1.96%Mn in Mass %) Was Deformed at 650 °C in Compression to Different Reductions, and Microstructural Evolution Was Investigated. During the Deformation, an Initial Lath Martensite Structure with a Complicated Morphology Was Gradually Changed into More Equiaxed Structure. After 50% Reduction and above, an Equiaxed, Fine Grained Structure Mainly Surrounded by High-Angle Boundaries Was Uniformly Formed with Dislocation Substructures, where the Dislocation Density in the Grains Is Relatively Low. Since there Was No Significant Boundary Migration during this Process, this Microstructural Evolution Can Be Termed as Continuous Dynamic Recrystallization.

Abstract: In this Study, Influences of P on the Microstructure, Mechanical Properties, and Retained Austenite Characteristics in Transformation Induced Plasticity (TRIP) Steels Were Investigated. Microstructure of 0.2mass%P Containing TRIP Steel Was Inhomogeneous and it Resulted in Deterioration of the Mechanical Properties. Retained Austenite Characteristics such as Volume Fraction and Carbon Concentration Were Also Affected by P. The Stability of Retained Austenite in P Containing TRIP Steel Was Different from that in P-Free TRIP Steel. Such Difference in the Stability of Retained Austenite Was Attributed to the Effect of the Carbon Concentration in Retained Austenite as Well as their Different Microstructure.

Abstract: With the Aim of Preparing the Raw Powders Used for Soft Magnetic Compacts Production, Nanocrystalline Soft Magnetic Powders of Fe_84.3Si₄B₈P₃Cu_0.7 Were Successfully Fabricated Using Crystallization by Rapid Heat-Treatment and Mechanical Ball-Milling Methods. We Investigated the Relation of the Magnetic Properties, Crystallization Degree and Heat-Treatment Condition in Salt-Bath Process. In this Study, a Fine Nanocrystalline Structure with an Extremely Number of α-Fe Grains with the Similar Size of ~ 30 nm Was Obtained. This Led to Excellent Soft Magnetic Properties, i.e., 1.85 T (197.7 emu/g) and 10 A/m for Saturation Magnetization and Coercivity, Respectively. By Controlling the Milling Time, Different Particle Size of Powder Can Be Obtained.

Abstract: The Plastic Deformation Behavior of a Biomedical Co–29Cr–6Mo–0.2N (wt.%) Alloy with a Fully γ (fcc) Matrix Was Studied by Compression Tests from Room Temperature to 1073 K. Serrated Stress–Strain Curves Caused by Dynamic Strain Aging (DSA) Was Clearly Observed at Temperatures of 773–973 K at a Strain Rate of 10⁻⁴ s⁻¹. Such a Flow Behavior Was Not Observed Significantly in other Conditions. Electron Backscatter Diffraction (EBSD) Analysis Revealed that Deformation Microstructures with DSA Occurrence Exhibited a Large Lattice Distortion over the Grains, while Local Strain Preferentially Increased in the Vicinity of Grain Boundaries in the Specimen Deformed at Room Temperature. Dislocations Were Dissociated into Stacking Faults (SFs) Bounded by Shockley Partial Dislocations both before and after Deformation; the DSA Observed in this Alloy Would Originate from the Interactions between Nitrogen Atoms and the Partial Dislocations/SFs.

Abstract: Structure of Zr₅₀Ni₅₀ Amorphous Alloy Was Analyzed by Anomalous X-Ray Scattering (AXS) Coupled with Reverse Monte-Carlo (RMC) Simulation. Topological Features in the Nearest Neighbor Atomic Configuration Clearly Suggest that the Strong Chemical Interaction between Ni and Zr Breaks the Icosahedral-Like Local Ordering Structure Common in the Dense Random Packing of Hard Sphere (DRPHS) Model. Nevertheless, the Structure of Zr₅₀Ni₅₀ Shows No Further Features Related to the Crystal-Like Chemical Short Range Ordering (CSRO).

Abstract: Strengthening by Grain Refinement and Increasing Dislocation Density through High-Pressure Torsion (HPT), which Is an Attractive Technique to Fabricate Ultrafine Grained and Nanostructured Metallic Materials, Is Expected to Provide β-Type Ti-29Nb-13Ta-4.6Zr (TNTZ) Higher Mechanical Strength while Maintaining Low Young’s Modulus because they Keep the Original β Phase. However, the Ductility Shows Reverse Trend. Greater Strength with Enhanced Ductility Can Be Achieved by Controlling Precipitated Phases through HPT Processing after Aging Treatment. Aged TNTZ Subjected to HPT Processing at High N Exhibits a Homogeneous Microstructure with Ultrafine Elongated Grains Having a High Dislocation Density and Consequently Non-Equilibrium Boundaries and Distorted Subgrains with Non-Uniform Shapes and Nanostructured Intergranular Precipitates of αphases. Therefore, the Effect of HPT Processing on the Microstructure and Mechanical Hardness of TNTZ after Aging Treatment Was Systematically Investigated in this Study. TNTZ, which Was Subjected to Aging Treatment at 723 K for 259.2 Ks in Vacuum Followed by Water Quenching, Subjected to HPT Processing at Rotation Numbers (N) of 1 to 20 under a Pressure of around 1.25 GPa at Room Temperature. The Microstructure of TNTZ_AT Consisted of Precipitated Needle-Like α Phases in β Grains. However, TNTZ_AHPT at N ≥ 10 Comprises Very Fine α and Small Amount ω Phases in Ultrafine β Grains. Furthermore, the Hardness of Every TNTZ_AHPT Was Totally much Greater than that of TNTZ_AT. The Hardness Increased from the Center to Peripheral Region of TNTZ_AHPT. In Addition, the Tensile Strength of Every TNTZ_AHPT Was Greater than that of TNTZ_AT. The Tensile Strength of TNTZ_AHPT Increased, but the Elongation Decreased with Increasing N and then both of them Saturated at N ≥ 10.

Abstract: In the Present Study, the Effects of the Microstructural Morphologies of a Ti-6Al-4V (Ti-64) Alloy on its Fatigue Behavior Were Investigated. Ti-64 Bars Were Subjected to Two Different Thermo-Mechanical Processing Methods. The First Sample, Referred to as Material-A, Had a Forged Microstructure with the Average Primary α Volume Fraction of 44%. The Second One, Referred to as Material-B, Had a Hot-Rolled Microstructure with the Average Primary α Volume Fraction of 43%. Fatigue Tests Were Performed on each Sample to Obtain S-N Curves. The Microstructure of each Sample Was Observed Using an Optical Microscopy in Order to Measure the Grain Sizes of the Primary α and Secondary α Phases. The Results of the Fatigue Tests Indicated that Material-B Demonstrates Better Fatigue Strength than Material-A. The Microstructure of the Longitudinal Section of each Material Was Also Observed to Analyze the Results of the Fatigue Tests. The Measured Diameters and Volume Fractions of the Primary α Phases of the Two Types of Materials Are Similar. On the other Hand, the Secondary α Width of each Material Is Different. It Is Found that Fatigue Strength Is Related to the Width of the Secondary α Phase.