Page 7 - Thesis_Lavrys
P. 7

7

                  provided  higher  tribotechnical  parameters  (wear  resistance,  friction  coefficient

                  and  temperature  near  the  friction  zone)  of  investigated  tribo-pairs  compared  to

                  ball burnishing or nitriding treatments.  It was established that the deformation-

                  diffusion treatment increases the wear resistance of VT22 titanium alloy in tribo-

                  pair  with  BrAZhN  10-4-4  bronze  twice  and  reduces  the  friction  coefficient  by

                  30% compared to nitriding without surface pre-deformation.

                         It  is  established  that  after  deformation-diffusion  treatment  the  fatigue

                  strength  approaches  the  values  after  strengthening  heat  treatment  of  VT22

                  titanium alloy. The fractographic analysis of the fracture surfaces of the studied

                  samples revealed a certain correlation, namely: the lower the fatigue strength of

                  the alloy samples after treatment, the larger area of brittle intergranular fracture

                  on the fracture surface.

                         It  is  shown  that  the  strength  of  samples  of  VT22  titanium  alloy  after  all

                  hardening treatments increases. The samples hardened by deformation-diffusion


                  treatment  were  somewhat  inferior  to  the  samples  after  cold  surface  plastic
                  deformation  and  nitriding  in  terms  of  the  ultimate  tensile  strength.  But,  the


                  plasticity  (elongation)  of  VT22  alloy  samples  after  deformation-diffusion
                  treatment was the highest. The nature of the fractures indicated the mechanisms


                  of ductile rupture, namely, the  formation  of the  so-colled dipole  void  structure
                  was fixed on fracture surface. A correlation was observed between the size and


                  depth of the voids (holes) in the surface fracture zone and the strength of VT22
                  alloys: the treatment that increases the strength the  most has the smallest  voids


                  (holes) on the fracture surface.

                         The  technological  recommendations  for  combined  deformation-diffusion

                  treatment of VT22 titanium alloy  were developed, which  provide the regulated

                  characteristics  of  hardened  layers  while  maintaining  the  volumetric

                  characteristics of the alloy.

                         Scientific novelty of the obtained results


                         1. The low-temperature range of the dependence of the parabolic constant of

                  nitriding rate was determined, and the activation energy of the process and other
   2   3   4   5   6   7   8   9   10   11   12