Characterization of Thermochemically Surface-Hardened Titanium by Light Optical Microscopy

Abstract

Thermochemically treated titanium grade 2 and 5 were investigated by light optical microscopy and hardness indentation. Gaseous oxidation in oxygen and N2O containing atmospheres resulted in a diffusion zone of oxygen in solid solution in titanium with a hardness up to 1000HV. A surface scale consisting of oxide can be present depending on the treatment conditions. A new type of carbo-oxidation treatment was applied, where carbon and oxygen are simultaneously incorporated into the surface. This resulted in new microstructural features such as a deep zone of mixed interstitial solid solution, i.e. a diffusion zone, and surface regions consisting of a mixed interstitial compound (TiCXO1-X structure). Carbo-oxidation yields hardness values in excess of 2500 HV in the mixed interstitial compound and values up to 1500 HV in the diffusion zone. Simultaneously, with the surface hardening treatment, core hardening of the material can be obtained.

Gaseous surface hardening of Ti-6Al-4V fabricated by selective laser melting

“…An applied pressure of 3 Pa yielded the highest surface hardness of 1670 HV corresponding to a compound composition of TiC0.63O0.37, as determined by X-ray diffraction (XRD). [7] Gammeltoft-Hansen et al [8] successfully carbo-oxidised both commercially pure titanium (Grade 2) and Ti-6Al-4V in a gaseous atmosphere containing only carbon and oxygen, confirming the formation of TiCxO1-x by XRD. The obtained hardness was approximately 2200 HV for the compound phase and 1500 HV in the diffusion zone for Ti grade 2.…”

“…The obtained hardness was approximately 2200 HV for the compound phase and 1500 HV in the diffusion zone for Ti grade 2. [8] Very recently, it has also been shown that three interstitial elements (nitrogen, carbon and oxygen) can be incorporated into the surface of titanium grade 2, resulting in a high total interstitial solid solubility. [9] A few examples of surface engineering of Ti-based AM components have been published.…”

Low Temperature Nitriding of Metal Alloys for Surface Mechanical Performance

“…Moreover, complex-shaped metal components are much cheaper than their equivalent ceramic ones. In this applicative domain, titanium alloys are by far the most interesting choice and can give rise to a tremendous amount of research (see, for example, [ 3 , 8 , 25 , 26 , 39 , 42 , 43 , 50 , 62 ]).…”

“…Nitriding can be achieved with a variety of techniques [ 3 ], the most popular ones being namely plasma, implantation, and gas or a combination of them (PBII) [ 4 ]. Nitriding methods have been applied to a number of different metals and alloys [ 5 , 6 , 7 , 8 , 9 , 10 ]. Below, we illustrate the mechanical strengthening achieved with steel and titanium alloys that have been the most successful.…”

Gaseous thermochemical synthesis and characterization of mixed interstitial phases in the Ti-C-O system

“…This can be alleviated by surface hardening of Ti by incorporation of interstitial elements, C, N and/or O, in the h.c.p. α crystal structure and via formation of interstitial compounds ( [1], [2], [3]). The solubility of carbon in α is maximally 0.08 wt% at 800 °C [4], higher contents entail formation of NaCl type δ carbide.…”