Aim: The study aimed to understand the interfacial bonding and diffusion of elements between substrate metal and HAcoated titanium implants in different plasma gas atmosphere. Materials and methods: Commercially pure titanium and Ti-6Al-4V substrate metals were coated with hydroxyapatite by plasma spray in plasma gas atmospheres of argon, argon/hydrogen, nitrogen, and nitrogen/hydrogen. The microstructure and interfacial bonding between the metal substrate and HA coating were studied by scanning electron microscopy, energy dispensive X-ray analysis (EDAX), and X-ray diffraction. Results: The analyses of the coatings obtained showed a different microstructural pattern of HA and diffusion of elements across the interface of metal and HA coating and chemical bonding for all plasma gas atmospheres. Conclusion: The plasma-coating atmosphere influences the microstructure and crystallization of HA. Diffusion of elements from metal substrate to HA coating and coating to metal surface indicate chemical bonding between the metal and coating in addition to usual mechanical bonding. Clinical significance: Bonding between the metal substrate and HA coating play a significant role in the stability of the dental implant. In addition to mechanical bonding, the plasma coated implants show some amount of chemical bonding at the interface.