On titanium alloys semiproducts quality control

Аuthors

Soldatenko I. V.

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

e-mail: iv_soldatenko@mail.ru

Abstract

The goal of the paper consists in titanium alloys semiproducts macrostructure quality evaluation technique improvement.

Active standard ten-point scale of macrostructures was developed based on – grains of strictly equiaxial shape specific to strain-free state of the alloy of sheet-like intragrain structure.

It is well know macrostructure we can see only those structure elements, which size exceeds 100 –150 micron (i. e. the ones exceeding the eye resolution capability).

Macro- and microstructure evaluation of a large number of serial semiproducts and laboratory samples revealed that not only – grains could be visible on a microstructure, but – colonies as well. It was established, that while checking a established, that the shape and size of the grains in the observed macrostructure depended on – grains and  – colonies in the microstructure.

Direct dependence of a macrostructure character from its microstructure was revealed. The paper shows that macro grain size and its tonality (degree of brilliance) depend directly on parameters of the microstructure, forming while deformation and heat treatment processes at temperatures of -or + – area. Correlation between the grain maximum longitudinal and diametrical sizes (the degree of non-equiaxiality – K) is clearly associated with physical degree of its deformation. This is another important parameter of macrostructure evaluation besides the grain size itself.

By deformation, the macro grain tonality or its degree of brilliance changes together with the macro grain shape. Interrelation between degree of brilliance of a macrostructure under study and with its microstructure was established.

The author suggests classify a macrostructure according to its tonality (degree of brilliance) by four types:

• Absolute brilliant – a typical macrostructure peculiar to allows with recrystallized or slightly malformed – grains which size exceeds 100 microns.

• Brilliant with fog elements – observed in alloys with medium degree of deformation (10-35%) in +  – area. Within on – grain one can observe micro areas withvarious degree of – phase spheroidizing development (from globular to practically non- spheroidized, plate-like shapes of the particles).

• Fog with brilliance elements – peculiar to the alloys malformed in +  – area to the degree of 40-55%. For the most part this structure is globular or globular plate-like. In some locations it preserves oriented character of – phase excreta, which in case of their large size are responsible for appearance of these brilliant locations in the macrostructure.

• Absolute fog-corresponds to globular or globular plate-like microstructure.

To improve titanium alloys evaluation objectivity and unambiguity the author suggest introduce quantitative estimation based on three parameters, namely grain size, and the degree of its non-equiaxiality and tonality.

The next step to titanium alloys production quality improvement consists in working out requirements to macrostructure based on quantitative estimation of its parameters.

Keywords:

titanium alloys, macrostructure, microstructure, structure parameters, grain size, non-equiaxial, tone value

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