CoatMat

Synthetic ferrous alloys containing chromium and/or nickel were prepared and borided at 1173 K with powders containing B4C, KBF4 and SiC for times varying from 20 to 60 h. The surface layers composed of borides of type (Fe, M)B and (Fe, M)2B were characterized by means of X-ray diffraction, microscopic observations, analysis with the microprobe and microhardness measurements. A quantitative study was carried out on the differentiated distribution of chromium and nickel in the phases constituting the borided layer.

The variation in hardness of the phases (Fe, M)B and (Fe, M)2B (M ≡ Cr or Ni), which are the predominant components of the borided layer obtained on iron alloys, was defined and related to increase in chromium, nickel and carbon contents. It was found that chromium increases the hardness both of the borided layer as a whole and of the boride components, even though these values are systematically lower than those measured on pure borides.

The chemical composition of sintered steels has been related to the physical and mechanical characteristics of the surface layers obtained by solid boronizing. Sintered samples of various composition and density were produced as bushings by mixing Hoganas powders and subsequent heating in industrial furnaces. Various conditions of temperature, time of treatment and chemical composition of the boriding agent were investigated. All the borided layers consisted of Fe//2B and FeB type borides.

The aim of this work was to ascertain if the alloying elements in steels influence the diffusion mechanism of the boron during boriding treatment and to relate the characteristics of the borided layer with the chemical composition of the matrix. Steels, Armco iron and some ferrous alloys containing Cr and/or Ni were borided for 7-24 hours at 1173-1223K using powders of composition B//4C equals 20 30%, KBF//4 equals 5%, SiC equals 65 75%. The borided samples were analysed by an X-ray diffractometer, electron microscope, EDS spectrometer, optical microscope and Vickers microdurometer.

The investigations were made on alloys OT-4 (Ti-3Al-1. 5 Mn), IMI318 (Ti-6Al-4V) and IMI550 (Ti-4Al-4Mo-2Sn-0. 5Si) of the alpha-beta type. The pressure was fixed at 10 torr and the temperature was made to vary between 800 and 1,000 degree C. A gaseous mixture was chosen, composed of 60 nitrogen and 40 hydrogen vol% and times of 4, 8 and 16 hours were selected for treatment with an ionic discharge. Diffractometric analysis was used for identification of the type of phases present on the hardened surface. It was found that the alloying elements modify the morphology of the surface layer.

Titanium metal and some of its alloys of the type Ti-Al-Me (Me=transition metal) were submitted to plasma nitriding. The resulting compound layer was examined by optical microscopy and by XR diffraction in order to establish both its microstructure and texture degree under different nitriding conditions. To this aim a texture evaluation method was employed, which was formerly devised and applied on surface layers obtained by boriding of steels. In these nitrided layers the Ti2N nitride was clearly textured while the TiN did not show an appreciable degree of preferred orientation of crystals.

Surface layers having elevated hardness were produced by ion nitriding of titanium and α-β alloys of Ti-6wt.%Al-4wt.%V, Ti-4wt.%Al-2wt.%Sn4wt.%Mo and Ti-4wt.%Al-2wt.%Mn. The treatment was conducted at temperatures between 1073 and 1273 K for times of 4-32 h, using gaseous mixtures of nitrogen and hydrogen containing 20-80 vol.% nitrogen. X-ray diffraction, optical microscopy and microhardness were used to characterize the hardened surfaces.