The coating was scrapped from Ti specimen's surface and investigated for its chemical structure using FT-IR spectroscopy. The powder was investigated by double-beam dispersive IR spectrometer (Nicolet iS10, Thermo Electron Corporation, UK) which utilized the selected range of 400 to 4000 wave numbers (cm⁻¹) at 4 cm⁻¹ resolution and averaging of 100 scans. Two milligrams of scrapped powder was mixed with 300 mg of KBr and pressed into a disc before the measurement.

Scanning electron microscope (SEM) (JSM 6300, JEOL, Japan) and energy dispersive spectroscope (EDS) were used to examine the morphological qualities and the elemental composition of the HA-Zn deposits. The working distance was 15 mm at 20 V. Three specimens were examined for each group of the study.

Specimens of control and HA-Zn coated groups were evaluated by a surface roughness profilometer tester (Surftest SJ-210, Mitutoyo Corporation, Tokyo, Japan,) according to ISO 4287-1997 [24] with a diamond tip radius of 5 μm, a scanning speed 0.5 mm/s, a resolution of 0.01 μm, a Gaussian filter, and a cut-off length of 8 mm. Seven specimens from each group were scanned and evaluated for the average roughness parameter, each specimen was scanned five times, and the mean was calculated in µm. The roughness parameter (Ra) values were compared for statistical significance using the Student t test in SPSS software version 20 (SPSS Inc. Chicago, IL, USA).

The adhesion of coating is qualitatively assessed by the tape test. A standard test method (Tape test-ASTM D 3359-97) was used for assessing the adhesion of the HA-Zn coating on the titanium substrate. In this method, a part of a pressure-sensitive adhesive tape (masking tape, M&G pen AJD97355) is pressed against the coating by the use of a pencil eraser for 90 s. The tape is then rapidly removed (without jerk movements) at 180° angle, and the degree of film removal is detected when the tape is pulled off. Because an integral coating with substantial adhesion is often not detached at all, the sternness of the test is typically improved by making a figure X cutting into the coat using a sharp scalpel with enough pressure to reach the metal substrate, then applying the tape and remove it. The denuded area is inspected for removal of coating from the substrate, and then the adhesion is ranked by relating the detached part of the coat versus a recognized rating scale. The test is repeated for three other locations in the same specimen. Coverage of coated substrate was computed using Matlab (version7.1) [25].