Effects of Bonding Agents on Metal-Ceramic Bond Strength of Co-Cr Alloys Fabricated by Selective Laser Melting

Abstract

Bonding agents have been developed to improve bond strength between ceramic and Co-Cr metal. The aim of this study was to investigate the influence of two bonding agents on bond strength of Co-Cr metal fabricated by selective laser melting (SLM). Bond strength was determined by a three-point bending test, and the interfaces of the metal and ceramic, before and after the bending test, were observed by optical microscopy and scanning electron microscopy (SEM) to determine the thickness of the oxide layer and amount of ceramic remaining. To analyze the elemental composition of the bonding agents and fractured surfaces, energy dispersive X-ray spectroscopy (EDS) was used. Co-Cr specimens with bonding agent showed significantly higher bond strength than Co-Cr specimens without bonding agents. The fractured surfaces of most specimens showed mixed failure, but failure mode varied according to bonding agent and fabrication type. Specimens from groups treated with bonding agents had significantly higher remaining ceramic fractions on fractured Co-Cr alloys than specimens from groups that did not receive bonding agent. Mass amounts of silicone (Si) and titanium (Ti) on the fractured alloy surfaces were also different among specimens according to method of fabrication and presence of bonding agent. Together, the results suggest that application of bonding agent to 3D printed Co-Cr metal increases bond strength with ceramics.

Keywords: bond strength; cobalt-chromium (Co-Cr) alloy; fracture failure mode; metal bonding agent; selective laser melting (SLM); three-point bending test.

Figure 1

Flow chart of the bond strength experiments.

Figure 2

Schematic diagram of metal-ceramic specimens conforming to ISO 9693 guidelines.

Figure 3

Schematic diagram of the three-point bending test.

Figure 4

Scanning electron microscopy images of the Co-Cr and ceramic interface after sputtering with Au due to the low conductivity of ceramic. (a) Casted specimen, magnification 200×; (b) casted specimen, magnification 1000×; (c) SLM-fabricated specimen without bonding agents, magnification 200×; (d) SLM-fabricated specimen without bonding agents, magnification 1000×; (e) SLM-fabricated specimen with bonding agent A, magnification 200×; (f) SLM-fabricated specimen with bonding agent A, magnification 1000×; (g) SLM-fabricated specimen with bonding agent B, magnification 200×; (h) SLM-fabricated specimen with bonding agent B, 1000×. The red arrows indicate the thick oxide layer that looks like a gap between ceramic and metal.

Figure 5

SEM images of specimens after the three-point bending test and before manual detachment of the ceramic portion. (a) Casted specimen, magnification 200×; (b) casted specimen, magnification 1000×; (c) selective laser melting (SLM)-fabricated specimen without bonding agents, magnification 200×; (d) SLM-fabricated specimen without bonding agents, magnification 1000×; (e) SLM-fabricated specimen with bonding agent A, magnification 200×; (f) SLM-fabricated specimen with bonding agent A, magnification 1000×; (g) SLM-fabricated specimen with bonding agent B, magnification 200×; (h) SLM-fabricated specimen with bonding agent B, magnification 1000×. Dotted lines represent the surface of the Co-Cr alloy. Yellow triangles indicate crack propagation and the large gap between the ceramic and metal layers. Red triangles indicate incomplete crack propagation.

Figure 6

Optical microphotographs of Co-Cr alloy surfaces after de-bonding with ceramic (magnification 8×). (a) Casted specimen; (b) SLM-fabricated specimen without bonding agent; (c) SLM-fabricated specimen with bonding agent A; (d) SLM-fabricated specimen with bonding agent B. Yellow triangles represent adherent ceramic, and red asterisks indicate remnant wash opaque. Blue circles indicate remnant sputtered Au.

Figure 7

Scanning electron microscopy images (300×) of specimens after de-bonding of ceramic from the Co-Cr alloy surface. (a) Casting group; (b) SLM-fabricated specimens without bonding agent; (c) SLM-fabricated specimens with bonding agent A; (d) SLM-fabricated specimens with bonding agent B. Red asterisks represent adherent ceramic. Yellow triangles show Co-Cr substrate fabricated by casting, and yellow circles indicate Co-Cr alloy fabricated by SLM. Blue diamonds indicate wash opaque from ceramic on the Co-Cr substrate, while green arrows indicate remnant Au from sputtering.

Figure 8

EDS analysis of the fractured Co-Cr and ceramic interface. (a) Casted group specimens; (b) SLM-fabricated specimens without bonding agent; (c) SLM-fabricated specimens with bonding agent A; (d) SLM-fabricated specimens with bonding agent B.