Depth of Transformation for Accelerated Aging in Y-TZP

Objective: A depth study was performed on yttria-stabilized-zirconia to observe the depth progression of transformation as a function of artificial aging time/treatment. Hypothesis: tested aging conditions of stabilized zirconia have the similar influence on depth progression of t → m transformation and cause the surface layer to transform first followed inward progression of transformation.

Methods: The aging treatments chosen were prolonged boiling (40 hours, 3.5 and 7 days) and autoclaving under 2 bar of pressure (1, 3, and 5 hours).  These tests efficiently accelerate the aging process of Y-TZP and provide observable patterns in the progression of transformation depth as time increases.  Transformation (t→m) was measured using Xray-diffraction – Siemens D 500 XRD device with Cu K-alpha radiation.  Scans were performed at 40 kV, 30 mA, 0.02 degrees/step from 27-33, with 12s/step dwell time.  Seven settings for the x-ray incident-angle were used to analyze the sample: 1,2,3,5,8,10, and varied (θ/2θ). 

 Results: Amount of monoclinic phase present and the corresponding x-ray incident angle and penetration depth is shown below.

Incident Angle	X-ray Penetration Depth (µm)	2-bar 5-Hour	2-Bar 3-Hour	2-bar 1-Hour	7-Day Boil	3.5-Day Boil	40-Hour Boil
Theta-2-Theta	6.05	17.54	14.3	3.61	32.6	21.0	13.7
1	0.85	52.2	53.2	13.7	57.2	59.1	39.8
2	1.65	45.4	42.0	8.90	51.6	56.4	30.0
3	2.35	38.8	39.3	8.22	47.8	50.6	26.5
5	3.55	29.3	36.7	5.73	41.3	34.7	20.2
8	4.95	22.7	18.9	4.28	36.3	27.2	16.9
10	5.55	20.1	17.5	3.98	33.0	23.4	14.5
Theta-2-Theta rerun	6.05	16.9	14.9	3.36	33.6	21.2	14.2

Conclusions: As the aging time was increased the t→m transformation increased.  The surface layer underwent the most transformation displaying decreasing transformation with depth progression.  This implies transformation saturation at the surface, which can lead to rougher surfaces.  Supported by NIDCR-5T32DE017607DART.