How to select the temperature / pressure range of a vacuum hot press according to the sintered material?
Release time:
2025-07-02
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Abstract
Selection of the temperature and pressure range of the vacuum hot press furnace according to the sintered material requires comprehensive consideration of the material properties, sintering mechanism and process objectives, the following are the key points:
Material melting point and thermal stability
The temperature is usually 0.5 to 0.9 times the melting point of the material (unit: absolute temperature). For example, tungsten (melting point 3422°C) needs to be above 2000°C, while alumina (melting point 2072°C) is usually 1400-1600°C. Non-oxides (e.g. SiC) need to avoid decomposition and be controlled below 1600-1800°C.
Diffusion and densification mechanisms
Metals/alloys: plastic deformation dependent, high pressure range (20~100MPa), e.g. titanium alloys commonly used 950~1100°C/30~50MPa.
Ceramics/refractory compounds: relies on diffusive mass transfer, lower pressure (10~50MPa), e.g. Al₂O₃ can be densified at 1400°C/10~20MPa.
Nanomaterials: low temperature sintering (0.4~0.6Tm) to avoid grain growth, pressure can be increased to 50~80MPa to promote particle rearrangement.
Phase transitions and chemical reactions
For example, ZrO₂ needs to stabilise the crystal shape (e.g. by adding Y₂O₃), and the sintering temperature needs to be precisely controlled (1350~1500°C); composites (e.g. TiB₂-TiC) need to avoid interfacial reactions, and may require rapid temperature increase or sectional pressurisation.
Process optimisation and experimental validation
Initial parameters can be estimated by theoretical models (e.g., Arrhenius equation) but need to be adjusted experimentally. For example, reaction intervals can be determined by thermogravimetric-differential thermal analysis (TG-DSC), and pressure-temperature curves can be optimised by small sample tests.
Equipment limitations and safety
Ensure that the furnace structure (e.g. graphite heater) can withstand the target temperature (e.g. 3000°C upper limit), and that the pressure system matches the material deformation resistance (e.g. ≥ 100 MPa for ultra-hard materials).
Example reference:
Silicon Carbide (SiC): 1900~2100°C/30~50MPa, vacuum or inert atmosphere;
Copper powder: 700~900°C/10~20MPa, low temperature to avoid volatilisation.
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2022-07-28
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