The study on the ion-nitriding (or ion-softnitriding) in the atmosphere of N
2-H
2 mixing gas (or N
2-H
2-C
3H
8 mixing gas) was previously carried out. In this report, NH
3 gas was added to the above-mentioned atmosphere, and the degree of dissociation of NH
3 gas, the thickness and composition of the compound layer and the depth of the diffusion zone were investigated (nitriding temperature: 550°C, nitriding time: 6 h, total gas pressure: 400 Pa (3 Torr), current density: 11.5 A/m
2). The main results were as follows.
(1) The degrees of dissociation of NH
3 gas as a function of its molar fraction in the introduced gases (NH
3-N
2-H
2 and NH
3-N
2-H
2-1%C
3H
8) were measured when the molar fraction ratio of N
2 to H
2 gases in the exhaust gases was kept constant as 1/3. Using the above measured degrees of dissociation of NH
3 gas, the molar fractions of NH
3, N
2, H
2 gases in the introduced gases (NH
3-N
2-H
2 and NH
3-N
2-H
2-1%C
3H
8) were well calculated to keep the molar fraction ratio of N
2 to H
2 gases in the exhaust gases as 2/1.
(2) When the molar fraction of NH
3 gas in the exhaust gases was increased, the voltage was increased and the thickness of the compound layer was also increased; however, the depth of the diffusion zone was almost constant.
(3) The volume ratio of the ε-Fe
2–3N phase to the sum of the ε-Fe
2–3N and γ′-Fe
4N phases in the compound layer,
cε⁄(
cε+
cγ′), was almost constant when the molar fraction ratio of N
2 to H
2 gases in the exhaust gases and the C
3H
8 gas content were constant. Here
cε and
cγ′ were the volume fractions of the ε-Fe
2–3N and γ′-Fe
4N phases in the compound layer.
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