In this paper, the effect of ball milling on Ti-based amorphous powders with nominal compositions of Ti48Cu39.5Ni10Co2.5 and Ti48Cu39.5Zr10Co2.5 (at. %) was studied. For this purpose, Ni and Zr containing crystalline master alloys were ball-milled for 20 hours in total. According to XRD analysis, the maximal amorphous fraction has been achieved in the case of Ni containing powder after 5 hours of milling. The nanocrystalline phase of CuTi3(Ni) having a grain size of 0.17-0.29 nm formed in the early stages of the milling process and remained stable until the end of milling. The amorphous-nanocrystalline transition of this phase is a reversible process. The amorphization process of Ti48Cu39.5Zr10Co2.5 is not so rapid than that in the Ni containing alloy system. This confirms that kinetic energy of the milling process is insufficient for destabilization of the Cu2ZrTi2 nanocrystalline (0.15-0.26 nm) phase. The microhardness of Ti48Cu39.5Ni10Co2.5 and Ti48Cu39.5Zr10Co2.5 particles was found to be HV0.01 519 ± 40 and 630 ± 55, respectively. For both compositions amorphous-nanocrystalline composites have been successfully obtained.

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The rebound hammer test of concrete can provide an alternative to drilled core tests for estimating the in-situ compressive strength of concrete. The variability of concrete strength is recognised during the strength assessment and the design strength of concrete is specified as its characteristic compressive strength by taking the variability of the strength of concrete into account. In the present paper, particular topics of the inherent variability of the rebound hammer tests are discussed. Different types of Schmidt hammers are compared in this sense. The precision of the original N-type Schmidt hammer is demonstrated to be superior to original L-type or Silver Schmidt N-type hammers. Observations are confirmed by normality tests. Results imply the need for further research. Measurement errors made by the operators of the rebound hammers are analysed. Differences among the repeatability and reproducibility are demonstrated. As a closing remark the need of revealing the connection between the variability of compressive strength and rebound index, as well as the need of the spatial variability analysis of rebound index are highlighted.

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Nanocrystalline/amorphous powder was produced by ball milling of Ti50Cu25Ni20Sn5 (at.%) master alloy. Both laser diffraction particle size analyzer and scanning electron microscope (SEM) were used to monitor the changes in the particle size as well as in the shape of particles as a function of milling time. During ball milling, the average particle size decreased with milling time from >320 µm to ~38 µm after 180 min of milling. The deformation-induced hardening and phase transformation caused the hardness value to increase from 506 to 779 HV. X-ray diffraction (XRD) analysis was used to observe the changes in the phases/amorphous content as a function of milling time. The amount of amorphous fraction increased continuously until 120 min milling (36 wt % amorphous content). The interval of crystallite size was between 1 and 10 nm after 180 min of milling with 25 wt % amorphous fractions. Cubic Cu(Ni,Cu)Ti2 structure was transformed into the orthorhombic structure owing to the shear/stress, dislocations, and Cu substitution during the milling process.