**2. Experimental**

The Ti powder used is a 99.4% purity Cp-Ti (grade 2) with nominal average particle size of 150 μm, produced by Alfa Aesar (product number: 10383), Kandel, Germany. The received (coded as "initial") powder was used as coarse-grained Ti, and the fine-grained Ti was produced from the same powder by use of high-energy ball milling. The milling was carried out with a Pulverisette 5 high-energy planetary ball mill (Fritsch, Idar-Oberstein Germany) at room temperature for 20 h. In order to prevent excessive cold welding, alcohol was used as a process control agent (PCA). The milling was performed in Ar atmosphere using a 250 mL hardened steel vial and hardened steel balls of 8 mm diameter. The ballto-powder (BPR) weight ratio and rotational speed were 30:1 and 200 rpm, respectively. The mixing of the initial and milled powders was also carried out with the same mill, but the milling parameters were changed to 10:1 BPR, 30 min and 100 rpm. Ethanol was not used in this case. During mixing, 2; 4; 6; 8 and 10 wt.% milled Ti was added to the initial Ti powder.

Instron 5982 (Norwood, MA, USA) equipment was used for the consolidation of the powders to green parts at ambient temperature. The mixed powders were placed in a hardened steel die between hardened steel punches to produce cylindrical specimens with a diameter of 8 mm and 8 mm height. Graphite 33 spray (Iffezheim, Germany) was used as lubricant on the die walls to decrease the friction, and during the cold uniaxial pressing, 1.6 GPa pressure was applied. The sintering of the green samples was carried out in an electric furnace (SF 16 type Three-Zone Split Tube Furnace, Norwood, MA, USA) in Ar 6.0 atmosphere (Siad Hungary, Miskolc, Hungary). Four different sintering temperatures were considered: 800, 850, 900 and 950 ◦C. The heating and the cooling rate were 100 ◦C/min and 1000 ◦C/min, respectively and the holding time was 60 min.

The morphology of the powders, the green samples and the sintered samples was investigated by Scanning electron microscopy (SEM) using a C. Zeiss EVO MA 10. and a Zeiss Crossbeam 540 LA-FIB SEM (Zeiss, Oberkochen, Germany). For the determination of APS values, an analysis of the SEM pictures was conducted; five SEM pictures representing different regions of the initial as well as the milled powder were analyzed, and the particle size (n = 100) was measured through the use of Image J 1.47 software [34].

The density of the samples in both green and sintered state was determined by measuring the weight and the dimensions of the samples. The microhardness (HV0.025) of the initial and milled powders was measured by an Instron Wilson Tukon 2100 B (Norwood, MA, USA). The hardness of the green and sintered samples was measured with the Brinell method (HB2.5/62.5) on a Wolpert UH930 machine (Illinois Tool Works Inc. Shanghai, China). Compression tests were carried out in order to determine yield, compression strength and the compression strain. These tests were conducted with Instron 5982 type (Norwood, MA, USA) universal material testing equipment, using a crosshead speed of 3 mm/min.
