Strengthening porous titanium fabricated by powder metallurgy via multi-step pressing technique

doi:10.1016/j.metadv.2026.02.016

Abstract

Abstract:

Conventional porous titanium suffers from insufficient strength and imprecise pore control. This work improved powder metallurgy process by employing a multi-step pressing (MSP) process with NH₄HCO₃ space holder to enhance pore structure and mechanical properties. Compared with one-step pressing (OSP), the MSP process significantly reduces microporous defects within pore walls and improves pore uniformity, sphericity, and large pore proportion. Thus, the MSP process effectively increases the load-bearing area of the pore wall via decreasing micropore defects and reduces stress concentration through enhancing the pore sphericality. This mechanism plays a crucial role in enhancing the strength of porous titanium. With 50% NH₄HCO₃ addition, the porosity of the MSP sample reached 51.9% and achieved elastic modulus of 6.9 GPa and compressive strength of 85 MPa, representing a 1.9% porosity reduction and 9.0% strength increase compared with OSP sample. MSP-produced porous titanium exhibited controllable porosity (24.9%-51.9%), elastic modulus (6.9-16.0 GPa) and compressive strength (85-178 MPa). These tailored properties closely match those of human bone, offering a promising strategy for high-performance medical implants.

Key words: Porous titanium, Powder metallurgy, Multi-step pressing technique, Pore characteristics, Mechanical properties

Yuhua Li, Qian Zhang, Yuxin He, Hongming Zhang, Haojie Wang, Yujing Liu, Shijie Liang, Pei Wang. Strengthening porous titanium fabricated by powder metallurgy via multi-step pressing technique[J]. Metals Advances, 2026, 45: 67-76.

Figures/Tables 12

Fig. 1. SEM morphologies and corresponding particle size distributions of (a), (b) Ti powder and (c), (d) NH4HCO3.

Table 1. Sample No., pressing process, NH4HCO3 addition, porosity and mechanical properties of the as-sintered porous titanium.

Sample No.	Pressing process	NH₄HCO₃ (vol.%)	Porosity (%)	Compressive strength (MPa)	Elastic modulus (GPa)
D1	OSP	0	8.9 ± 0.5	1850 ± 23	54.8 ± 1.8
D2	OSP	20	28.9 ± 2.1	165 ± 9	16.1 ± 1.1
D3	OSP	30	35.3 ± 3.0	131 ± 11	12.0 ± 0.9
D4	OSP	40	43.6 ± 3.8	105 ± 8	9.9 ± 0.7
D5	OSP	50	52.9 ± 4.5	78 ± 9	6.7 ± 0.9
E1	MSP	0	7.7 ± 0.4	2250 ± 18	78.6 ± 2.3
E2	MSP	20	24.9 ± 1.9	178 ± 11	16.0 ± 1.5
E3	MSP	30	32.2 ± 2.8	145 ± 8	11.9 ± 1.1
E4	MSP	40	40.2 ± 3.4	118 ± 10	9.7 ± 0.8
E5	MSP	50	51. 9 ± 4.2	85 ± 8	6.9 ± 0.4

Fig. 2. XRD patterns of the as-sintered porous titanium.

Fig. 3. OM microstructures of the as-sintered porous titanium: (a), (c), (e), (g), and (i) corresponding to OSP samples D1−D5; (b), (d), (f), (h), and (j) corresponding to MSP samples E1−E5.

Fig. 4. Relationship between porosity and space holder addition of the as-sintered porous titanium under OSP and MSP processes.

Fig. 5. Pore morphologies of the as-sintered porous titanium: (a), (c), (e), (g), and (i) corresponding to OSP samples D1−D5; (b), (d), (f), (h), and (j) corresponding to MSP samples E1−E5.

Fig. 6. Proportions of macropores and micropores of the as-sintered porous titanium.

Fig. 7. Pore size distribution of the as-sintered porous titanium under OSP and MSP processes: (a) OSP sample D1 and MSP sample E1, (b) OSP samples corresponding to D2−D5, (c) MSP samples corresponding to E2−E5.

Fig. 8. Roundness distribution of the as-sintered porous titanium under OSP and MSP processes: (a) OSP samples corresponding to D1−D5, (b) MSP samples corresponing to E1−E5.

Fig. 9. Average distribution statistics of (a) pore size and (b) roundness for the as-sintered porous titanium under OSP and MSP processes.

Fig. 10. (a) Engineering stress-strain curves of the as-sintered porous titanium, and the insets represent the macroscopic compressive sample images of D1 and E1 before and after the compression test, (b) mechanical properties, (c) a local magnification of red frame area in (a), (d) mechanical properties with a local magnification in (b).

Fig. 11. SEM fracture morphologies of the as-sintered porous titanium: (a)−(d) OSP samples corresponding to D2−D5, (e)−(h) corresponding enlarged images of D2−D5, (i)−(l) MSP samples corresponding to E2−E5, (m)−(p) corresponding enlarged images of E2−E5.

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