PSI - Issue 50

N.B. Pugacheva et al. / Procedia Structural Integrity 50 (2023) 251–256 N.B. Pugacheva et al./ Structural Integrity Procedia 00 (2022) 000 – 000

252

2

composite, which determines liability to cracking under external mechanical loads. The use of copper and its alloys as matrices of SHS composites for electrotechnical and heat exchanging parts and structural components is of interest – Pacheco et al. ( 2007). The relatively low melting temperature of copper (1083 °С) provides the maximum closeness of the values of real density to those of theoretical one after additional hot compaction. Earlier studies by Pugacheva et al. (2019) and Pugacheva et al. (2021) reported that the structural constituents resulting from synthesis are unevenly distributed in the volume of the composite. This causes the uneven distribution of micromechanical prop erties in the composite volume. The aim of this study is to correlate the micromechanical properties of the Сu Ti-C-B composite and the fracture pattern in transverse bending tests. 2. Materials and methods Powders of Ti, Сu, C, and В 4 С were selected as the s tarting materials for synthesis. The powders were mixed in a ball mill for 12 hours and poured into a steel pipe acting simultaneously as an open-type reactor and the outer shell of a plate. The plate was then placed into an electric oven and heated to the temperature of the onset of exothermal reactions (1020 °С). The copper powder forms the metal matrix of the composite. The Ti, C, and B 4 С powders are temperature-control components (TCC) providing an exothermic reaction. Ti C BC TiC TiB Q      2 4 2 2 4 . (1) The content of the TCCs in the starting mixture was calculated from the condition for the occurrence of reaction (1) in stoichiometric proportions. The fraction of the TCCs in the starting mixture was 25 %. Immediately after the synthesis had been completed, t he specimens were hot compacted by a hydraulic press at 900 °C under a load of 250 MPa. As a result, a sandwich was produced, i.e. a plate with an outer steel shell inside which there is a synthesized composite. The microstructure, chemical and phase compositions of the produced composite were studied on the cross cuts of the sandwich plates by means of a Tescan Vega II XMU scanning electron microscope with Oxford energy dispersive and wave dispersive (for boron content determination) attachments. The phase X-ray diffraction analysis was performed by means of a Shimadzu X-ray diffractometer in Cr K α radiation. Rockwell hardness of the composite was measured by HRC. The density of the specimens was determined by hydrostatic weighing in the air and in distilled water with a density of 998 kg/m 3 by means of an Ohaus Pioneer PA 214 analytical balance. The micromechanical properties of the composite were determined according to ISO 14577-1:2015. Instrumented indentation with plasticity diagram recording was performed by means of a Fischerscope HM2000 XYm measurement device with the use of a Vickers indenter and the WIN-HCU software at a maximum load of 0.980 N, a loading time of 20 s, a load holding time of 15 s, and an unloading time of 20 s. The error in the microhardness and microindentation characteristics for 10 measurements was calculated with the confidence factor p = 0.95. The following micromechanical characteristics were determined from the indentation results: Vickers microhardness (НV), contact elastic modulus (Е*), the component of the work of plastic deformation during indentation ( φ ), indentation creep (С IT ), the share of elastic deformation in the total indentation deformation H IT /E*, where HIT is indentation hardness at the maximum load. The values of φ and С IT were calculated by the following formulas:

100%   

1     

W W

(2)

,



t e

max h h h 

(3)

,

100%

С IT

1





1

where W e is the work of elastic deformation during indentation, released at unloading, nJ; W t is the total mechanical work during indentation, defined by the area under the loading curve, nJ; h 1 is indenter penetration depth corresponding to the initial point of the horizontal portion in the loading curve, μm; h max is the maximum indenter penetrat ion depth, μm.