Molybdenum (Mo) plates, characterized by their high melting point (2623°C), exceptional thermal conductivity, and low coefficient of thermal expansion, are critical materials in high-temperature applications such as semiconductor crucibles, aerospace components, and nuclear reactors. However, their body-centered cubic (BCC) structure and inherent brittleness at room temperature present significant challenges in mechanical machining. This study synthesizes recent research on the deformation behavior, texture evolution, and fracture mechanisms of Mo plates during thermomechanical processing, providing insights into optimizing machining parameters for ductility and dimensional accuracy.
Molybdenum’s unique combination of properties—including high modulus of elasticity (330 GPa) and yield strength (655–795 MPa)—makes it indispensable in extreme environments. Yet, its low plasticity at ambient temperatures and high deformation resistance necessitate specialized processing techniques. Recent advancements in hot spinning, cross-rolling, and alloy modification have expanded the machinability envelope of Mo plates, enabling near-net-shape forming with reduced residual stresses.
1. Thermomechanical Processing and Microstructural Control
1.1 Hot Spinning and Annealing Effects
Studies on hot power spinning of Mo plates for sapphire crucibles reveal that controlled deformation parameters—such as spinning temperature (1200–1500°C), roller feed rate (0.5–2.0 mm/rev), and wall thinning rate (10–30%)—dictate microstructural evolution. Transmission electron microscopy (TEM) analysis shows that dynamic recrystallization occurs above 1300°C, forming equiaxed grains that enhance ductility. Post-spinning annealing at 1600°C for 2 hours eliminates work-hardened layers, reducing fracture susceptibility during subsequent machining.
1.2 Cross-Rolling and Texture Engineering
Cross-rolling techniques, which alternate rolling directions between passes, induce a dominant {001}<110> rotated cube texture in Mo plates. This texture, verified by X-ray diffraction (XRD), improves yield strength by 15–20% in the rolling direction (RD) while maintaining 10–12% elongation. When total deformation exceeds 96%, the γ-fiber texture weakens, minimizing anisotropic behavior critical for precision machining.
2. Fracture Mechanisms and Ductility Enhancement
2.1 Laminar Fracture in Pure Mo
Fractographic analysis of deformed Mo plates shows that ductile fracture proceeds via laminar separation, where individual laminae delaminate under shear stress. This mechanism, observed in 90% reduced plates, correlates with subgrain rotation and the formation of microbands. Adding 0.5–1.0 wt% hafnium carbide (HfC) disrupts brittle cleavage planes, shifting fracture modes to mixed ductile-brittle with characteristic slip steps.
2.2 Alloying Strategies for Toughness
NASA research on Mo-Hf-C alloys demonstrates that HfC precipitates (≤1 μm) pin grain boundaries, increasing fracture toughness by 30% without sacrificing high-temperature strength. The optimal strengthening effect occurs at 0.8 wt% HfC, where precipitate spacing matches the subgrain size (~5 μm).
3. Machining Optimization Guidelines
3.1 Turning and Milling Parameters
- Cutting Speed: 15–25 m/min (coated carbide tools)
- Feed Rate: 0.05–0.15 mm/rev (to avoid built-up edge formation)
- Depth of Cut: ≤0.5 mm (prevents chipping at tool edges)
- Coolant: High-pressure oil-based lubricants (to dissipate 80–90% of cutting heat)
3.2 Surface Integrity Considerations
- Residual stresses from machining can reach −200 to −300 MPa compressive values. Stress relief annealing at 1100°C for 1 hour reduces these stresses by 70–80%.
- Surface roughness (Ra) values of 0.6–1.2 μm are achievable with diamond-coated tools, critical for vacuum applications.
4. Future Directions
Emerging research on MoS₂-doped Mo composites suggests that 2D layered structures could enhance lubricity during machining. Preliminary studies indicate a 40% reduction in cutting forces when MoS₂ platelets align parallel to the cutting direction. Additionally, additive manufacturing of Mo preforms may enable near-net-shape components, minimizing material waste in aerospace and nuclear applications.
The mechanical machinability of Mo plates hinges on balancing thermomechanical processing routes with alloy design. By leveraging cross-rolling textures, controlled annealing, and nanostructured precipitates, manufacturers can achieve a 15–20% improvement in machinability while preserving 95% of the material’s high-temperature strength. Future advancements in composite architectures and hybrid manufacturing techniques will further expand the applicability of Mo plates in extreme-environment technologies.