Surface treatment method of metallic materials

Abstract

A surface treatment method of metallic materials provided by the present invention includes steps of: (S1) cleaning a surface of an initial metallic material to be treated, and then drying; and (S2) placing the dried metallic material in a heating furnace, adjusting a vacuum degree inside the heating furnace to a preset value under the protection of a mixed flowing gas of oxygen and an inert gas, heating and preserving, cooling to room temperature by furnace cooling, and completing the surface treatment of the metallic material to be treated, wherein the heating temperature is larger than the destruction temperature of the native oxide at the surface of the initial metallic material. The present invention is able to increase the surface hardness of the metallic material within a large depth, and has the advantages of low processing cost, high efficiency, good controllability, convenient operation and low surface contamination for the workpiece.

Claims

1. A surface treatment method of metallic materials, comprising steps of: (S1) cleaning a surface of an initial metallic material to be treated, and then drying; and (S2) placing the dried metallic material in a heating furnace, adjusting a vacuum degree inside the heating furnace to a preset value under a protection of a mixed flowing gas of oxygen and an inert gas, forming an oxide layer at a topmost surface of the dried metallic material while forming a solid solute oxygen beneath the oxide layer with a content of gradient distribution in the dried metallic material by heating and preserving, and cooling to a room temperature by furnace cooling, thereby completing a surface treatment of the metallic material to be treated, wherein: a heating temperature is in a range of 650° C.-1000° C. with a corresponding preserving time larger than 10 h; or a heating temperature is equal or larger than 1000° C. with a corresponding preserving time larger than 1 h; after cooling to the room temperature by furnace cooling, the step of (S2) further comprises removing the oxide layer and cleaning a surface of the removed metallic material; the oxide layer on the surface of the cooled metallic material is removed by at least one process selected from the group consisting of mechanical grinding, turning, pickling, and electrolytic polishing, so that no oxide phase is left at a topmost surface of the cooled metallic material; the initial metallic material is vanadium, niobium, tantalum, chromium, molybdenum, magnesium, zirconium, iron, vanadium alloy, niobium alloy, tantalum alloy, chromium alloy, molybdenum alloy, magnesium alloy, zirconium alloy, or steel; when the initial metallic material is the vanadium alloy, the niobium alloy, the tantalum alloy, the chromium alloy, the molybdenum alloy, the magnesium alloy, the zirconium alloy, or the steel, a content of vanadium, niobium, tantalum, chromium, molybdenum, magnesium, zirconium, iron in the vanadium alloy, niobium alloy, tantalum alloy, chromium alloy, molybdenum alloy, magnesium alloy, zirconium alloy, or steel exceeds 5 at. % (atomic percentage), respectively; a volume content of the oxygen in the mixed gas formed by the oxygen and the inert gas is in a range of 0.2% to 5%; the vacuum degree inside the heating furnace is adjusted to 250 Pa-10.sup.5 Pa under the protection of the mixed flowing gas of the oxygen and the inert gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flow chart of the present invention.

(2) FIG. 2 is a bright field TEM (transmission electron microscope) image of a metallic material according to a first embodiment of the present invention.

(3) FIG. 3 is a cross-sectional hardness distribution chart of the metallic material according to the first embodiment of the present invention.

(4) FIG. 4 is a cross-sectional hardness distribution chart of the metallic material according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(5) The present invention will be further described in detail below with accompanying drawings as follows.

(6) Referring to FIG. 1 of the drawings, a surface treatment method of metallic materials provided by the present invention comprises steps of:

(7) (S1) cleaning a surface of an initial metallic material to be treated, and then drying; and

(8) (S2) placing the dried metallic material in a heating furnace, adjusting a vacuum degree inside the heating furnace to 10.sup.−3 Pa-10.sup.5 Pa under a protection of a mixed flowing gas of oxygen and an inert gas, heating and preserving with a preserving time larger than 1 min, cooling to a room temperature by furnace cooling, removing an oxide layer on a surface of the cooled metallic material, cleaning a surface of the removed metallic material, and completing a surface treatment of the metallic material to be treated, wherein a heating temperature is larger than a destruction temperature of a dense and native oxide at the surface of the initial metallic material.

(9) Preferably, the metallic material is vanadium, niobium, tantalum, chromium, molybdenum, magnesium, titanium, zirconium, iron, vanadium alloy, niobium alloy, tantalum alloy, chromium alloy, molybdenum alloy, magnesium alloy, titanium alloy, zirconium alloy, or steel, wherein: a content of vanadium, niobium, tantalum, chromium, molybdenum, magnesium, titanium, zirconium, iron in the vanadium alloy, niobium alloy, tantalum alloy, chromium alloy, molybdenum alloy, magnesium alloy, titanium alloy, zirconium alloy, and steel exceeds 5 at. %, respectively.

(10) Preferably, a volume ratio of oxygen in the mixed gas formed by the oxygen and the inert gas is in a range of 0.01% to 100%.

(11) Preferably, the oxide layer on the surface of the cooled metallic material is removed by at least one process selected from a group consisting of mechanical grinding, turning, pickling, and electrolytic polishing.

First Embodiment

(12) Take a metallic pure niobium rod with a diameter of 4 mm and a length of 8 mm, cut a surface of the niobium rod with a grinding machine, and clean the cut niobium rod with acetone, place the cleaned niobium rod in a tube furnace, introduce a mixed gas of oxygen and argon gas with a flowing rate of 1000 sccm into the tube furnace, wherein a volume ratio of oxygen in the mixed gas is 0.2%, remain a vacuum degree inside the tube furnace to be 250 Pa through controlling a pumping speed of a mechanical pump, heating to 1000° C. at a heating rate of 10° C./min and preserving for 1 h, cooling to a room temperature via furnace cooling, removing an oxide layer on a surface of the cooled niobium rod by grinding with sandpaper, and finally obtain a treated sample.

(13) Referring to FIG. 2, the obtained sample is characterized by transmission electron microscopy at a position 20 μm away from the topmost surface, and only defects such as dislocation loops which are introduced by the preparation process of the TEM (transmission electron microscope) sample or initially stored inside initial sample can be observed. Obviously, there is no oxide structure formed either at the grain boundary or inside the grain interior.

(14) Referring to FIG. 3, the obtained sample is cut in the middle, and a hardness distribution thereof is measured from a surface to a core along its radial direction and then the hardness distribution of the obtained sample is compared with an initial sample. As can be seen in FIG. 3, the hardness of the obtained sample is significantly improved within the depth of 1.3 mm from the surface thereof, and gradually decreased from the surface to the core with a gradient distribution. In addition, the hardness at the surface of the obtained sample is 3.5 times that of the initial sample.

Second Embodiment

(15) Take a metallic pure vanadium sheet with a thickness of 1.2 mm, place the vanadium sheet in a tube furnace, introduce a mixed gas of oxygen and argon gas under normal pressure into the tube furnace, wherein a volume ratio of oxygen in the mixed gas is 5%, heating to 650° C. at a heating rate of 10° C./min and preserving for 10 h, cooling to room temperature by furnace cooling, and finally obtaining a sample.

(16) Referring to FIG. 4, a surface of the obtained sample is continuously ground and polished to remove the oxide layer obtained by oxygen permeation from the upper surface of the vanadium sheet, and the cross-sectional hardness from the side surface to the core of the obtained sample is measured. It can be seen from FIG. 4 that significant hardening occurs in the range of 450 μm away from the side surface of the obtained sample. In addition, the hardness at the surface of the obtained sample is five times that of the core of the obtained sample, and gradually decreases from the side surface to the core with a gradient distribution.

(17) In addition, those skilled in the art can make other changes within the spirit of the present invention, and these changes in accordance with the spirit of the present invention should be included in the protective scope of the present invention.