How to Determine The Process Parameters for Vacuum Hot Pressing Sintering Based on Powder Characteristics
Release time:
2025-07-14
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Abstract
The process parameters of vacuum hot pressing sintering (temperature, pressure, holding time, vacuum degree, etc.) need to be optimized according to the physical and chemical properties of the powder to ensure efficient densification and ideal performance. The following are the key factors and selection methods:
1. Characteristics of powder particles
(1) Particle size and morphology
Fine powder (<10 μ m): with a large specific surface area and high sintering activity, it can lower the sintering temperature (0.5-0.7 Tm), but is prone to agglomeration and requires uniform pressing.
Coarse powder (>50 μ m): requires higher temperature (0.7~0.9 Tm) or pressure (50~100 MPa) to promote diffusion.
Appearance: Spherical powder has good flowability but low sintering activity, requiring higher temperatures; Irregular powder is easy to press but may require pre pressing molding.
(2) Powder purity
Impurities or oxides (such as SiO ₂ in Al ₂ O ∝) may lower the sintering temperature (liquid-phase sintering), but it is necessary to control and avoid performance degradation.
2. Material category and sintering mechanism
(1) Metal powders (such as Ti, Cu)
Temperature: 0.6~0.8 Tm (titanium: 900~1100 ℃, copper: 600~800 ℃).
Pressure: 10-50 MPa (low pressure for soft metals, high pressure for refractory metals such as W/Mo).
Vacuum degree: ≤ 10 ⁻³ Pa (to prevent oxidation).
(2) Ceramic powders (such as Al ₂ O3 SiC）
Temperature: 0.7~0.9 Tm (Al ₂ O ∝: 1400~1600 ℃, SiC: 1800~2000 ℃).
Pressure: 30-100 MPa (high pressure is required for covalent bonding ceramics).
Additive: Adding MgO/Y ₂ O3 can lower the sintering temperature.
(3) Composite powders (such as WC Co)
Temperature: Near the melting point of cobalt phase (1300-1400 ℃) to promote liquid-phase sintering.
Pressure: 20-50 MPa, to avoid segregation.
3. Optimization of process parameters
Heating rate: fine powder/nano powder needs to be slow (5~10 ℃/min) to prevent cracking.
Insulation time: usually 10~60 minutes, nanomaterials can be shortened (5~20 minutes).
Timing of pressure application: Low temperature pressure (<0.5 Tm) is beneficial for particle rearrangement, while high temperature pressure promotes densification.
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2022-07-28
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