Preparation of High-Strength Pure Titanium by Powder Metallurgy: One-Step Pressing Versus Multi-Step Pressing Technique

doi:10.1007/s40195-025-01911-4

Abstract

Abstract:

Pure titanium fabricated by powder metallurgy generally encounters problems including low relative density and low strength, which limits its application performance. This work proposed a multi-step pressing (MSP) technique for developing high-strength pure titanium. The MSP processes of spherical Ti powders of 15-53 μm, 53-105 μm, and 75-180 μm were systematically investigated through multi-particle finite element method (MPFEM) compared with conventional one-step pressing (OSP) technique. The relative density, phase constitution, microstructure, and compressive mechanical properties of the sintered bulk pure titanium were characterized. Simulation results demonstrate that the MSP technique significantly increases the relative density of green compacts by 3.2%, 3.3%, and 5.2%, respectively, compared with OSP technique. Experimental results indicate the relative density of the sintered specimens prepared by MSP spherical powders increases by 5.4%, 4.5%, and 4.5%, respectively, compared to OSP, and the yield strength improves by 16%, 13%, and 18%. For the sintered specimens prepared by MSP irregular powder of 15-53 μm, the relative density increases by 6.0% and the yield strength increases by 15%. The enhancement of relative density and yield strength is mainly because the MSP technique mitigates stress concentration between powder particles. Compared to spherical powder, irregular powder exhibits stronger mechanical interlocking owing to the greater propensity for displacement and deformation, which facilitates mutual wedging and interlocking, resulting in superior strength performance.

Key words: Pure titanium, Powder metallurgy, Multi-particle finite element method, Pressing technique, Mechanical properties

Yuhua Li, Yuxin He, Qian Zhang, Chuanwei Zhang, Libin Niu, Yujing Liu, Saisai Zhu, Pei Wang. Preparation of High-Strength Pure Titanium by Powder Metallurgy: One-Step Pressing Versus Multi-Step Pressing Technique[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(10): 1839-1852.

Figures/Tables 13

Fig. 1 a-c Initial packing structure, d powder pressing model with particle size of 15-53 μm

Table 1 Material parameters of Ti used in the simulation

Material	Young’s modulus (GPa)	Poisson’s ratio	Strength coefficient (MPa)	Density (g cm⁻³)
Ti	109	0.33	275	4.51

Fig. 2 a-d SEM morphologies, e-h particle size distributions of Ti powders

Fig. 3 OSP and MSP process curves

Table 2 Mechanical properties, average grain size, and C, O, and N contents of the as-sintered samples

Pressing process	Powder shape	Particle size (μm)	Sample No	E (GPa)	${\sigma }_{0.2}$ (MPa)	Average grain size (μm)	C (wt%)	O (wt%)	N (wt%)
OSP	Irregular	15-53	S1	58.3 ± 3.2	1115 ± 10	26.2 ± 0.8	0.056	1.01	0.15
	Spherical	15-53	S2	26.7 ± 6.1	319 ± 15	39.5 ± 0.7	0.022	0.08	0.026
		53-105	S3	21.6 ± 4.8	276 ± 8	56.3 ± 1.2	0.019	0.10	0.018
		75-180	S4	17.0 ± 4.1	232 ± 13	72.7 ± 1.3	0.024	0.07	0.016
MSP	Irregular	15-53	S5	66.7 ± 5.9	1281 ± 12	25.6 ± 0.4	0.059	1.03	0.12
	Spherical	15-53	S6	34.5 ± 3.7	369 ± 6	30.4 ± 0.9	0.027	0.13	0.021
		53-105	S7	30.5 ± 6.2	312 ± 14	51.0 ± 0.9	0.021	0.09	0.014
		75-180	S8	26.3 ± 7.7	274 ± 12	76.2 ± 1.1	0.027	0.09	0.019

Fig. 4 a Relative density and pressure ($\rho$-P) relationship for spherical Ti powders with different particle sizes during OSP process, b Heckel fitting curves, c relative density under OSP and MSP processes

Fig. 5 Equivalent von Mises stress distribution of the spherical Ti powder particles under the OSP process

Fig. 6 a-c Equivalent von Mises stress distributions of spherical Ti powder particles with different sizes under the MSP process, d maximum stress (σmax) and high stress proportion for the spherical Ti powder particles under the OSP and MSP processes

Fig. 7 Equivalent plastic strain distribution of the spherical Ti powder particles under the OSP process

Fig. 8 XRD patterns of the as-sintered samples

Fig. 9 OM morphologies of the as-sintered samples prepared by OSP

Fig. 10 OM morphologies of the as-sintered samples prepared by MSP

Fig. 11 a Engineering stress-strain curves, b mechanical properties for the as-sintered samples

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