PSI - Issue 13

S.A. Atroshenko et al. / Procedia Structural Integrity 13 (2018) 1359–1361 Author name / Structural Integrity Procedia 00 (2018) 000–000

1360

2

scale, in units of milli-Joules per square meter (mJ/m 2 ). The SFE is related to the preferred mechanism through which the plastic deformation occurs in closed-packed metals. Plastic deformations in closed-packed metals may occur through different mechanisms including dislocation gliding, twinning and phase transformation. The SFE is a crucial parameter for understanding plastic deformation of closed-packed metals, since it governs the activation of these mechanisms. Although dislocation gliding is present everywhere, it is the dominant mechanism where the SFE is quite high. Under high strain rate deformation a distinct rise in temperature due to adiabatic deformation heating can raise the SFE either towards, or off the optimum value for twinning, depending on the initial SFE value. 2. Materials and experimental technique Aluminum and copper of technical purity, EI-961 chromium steel (0.11C; 11Cr; 1.5Ni, 1.6W; 0.18V; 0.35Mo; 0.025S; 0.03P) and Grade 5 Ti alloy (or Ti-6Al-4V) samples were examined. In this study the abrasive powder was accelerated by an air flow in a small-scale wind tunnel (Petrov et al. (2017), Evstifeev et al. (2018), Atroshenko et al. (2017)). Fig. 1 schematically shows the experimental setup. The velocity of the air flow is controlled by pressure in the system. Relation between air pressure and flow velocity is known due to calibration procedures. A special feeder device is used to mix abrasive particles into the air flow providing possibility to control concentration of the abrasive particles. The experiment duration is set with a remotely controlled sample inlet system. Thus, all basic parameters of the erosion experiment were controlled and therefore various conditions were obtained. All the tests were performed at room temperature and the impingement angle was equal to 90 degrees.

Fig. 1. Scheme of the experimental setup: 1 – compressor room, 2 – airflow acceleration pipe, 3 – solid particles feeder device, 4 – sample inlet device, 5 – holder with a mounted sample, 6 – working chamber.

The fracture surface of specimens after erosion test for different materials was studied on an Axio-Observer Z1-M optical microscope in the dark field. The viscous fracture surface is characterized by a dim grey appearance with characteristic “fibers.” The brittle fracture surface is crystalline without visible signs of plastic deformation on the fracture surface. The percentage of the viscous fracture component S (shear area) (in %) was determined according to the ASTM E 436-03. 3. Results and discussions The results of measuring the percentage of fibers S on the fracture surface are given in table 1. As can be seen from the presented data, the destruction of the AD1 aluminum alloys after dynamic erosion was the most brittle than other investigated metals. The most ductile fracture among all investigated metals has copper. A deeper penetration of particles in the erosion is observed for AD1 aluminum alloy samples (Fig.2a), comparing to Ti alloy, steel and copper as it is seen from Fig.2. The thickness of the damaged layer is the largest in AD1 aluminum alloy and smaller in the other materials.

Table 1. An example of a table.

Material

lattice BCC FCC FCC

SFE, mJ/m2

Air flow / powder V, m/s Powder, µm

T, sec

Shear, %

Steel (EI-961) Aluminum (AD1)

100 Gholizadeh (2013) 100/74 210 Gholizadeh (2013) 100/74

109 300 109 300 109 300 109 300

92.7 90.2 99.4 96.0

Cu

85 Gholizadeh (2013) 148 Angyang (2016)

100/74 100/74

Ti alloy

HCP+BCC