DD144930B1 - METHOD FOR PRODUCING DIFFUSION-LINKED DOUBLE LAYERS - Google Patents

Description

-A-

Process for the preparation of diffusion bonded double layers

Field of application of the invention

The invention relates to a method for producing diffusion-bonded double layers consisting of a titanium carbide interlayer and a titanium boride surface layer on K 10 and K 2Q cemented carbide bodies, in particular on cutting inserts for metal cutting machining ·

Characteristic of the known technical solutions

It is known to increase the wear resistance of hard metal moldings, such as indexable cutting inserts or other carbide tool inserts and wearing parts, by surface treatment methods.

These methods include surface coatings of pure hard materials such as carbides, borides, urides, and silicides of Gs, Vs and VIs. Lifting group of the periodic system, alpha-AlgO-, and similar, from hard material mixed crystals, such as carbonitrides or mixed carbides or from several

Layered layers and layer combinations · such hard materials and mixed hard crystals with abrupt or continuous transitions with each other and the hard metal body.

The production of these layers is preferably carried out by chemical vapor deposition in the temperature range between 1150 and 1500 K using normal or low pressure.

In order to improve the adhesion between the hard coating and the substrate (hard metal base body), diffusion treatments are proposed following the layer deposition. The deposition conditions are selected for producing particularly impact-resistant layers such that the hard material coating reacts with hard materials of the substrate with formation of mixed crystals.

The thickness of the hard coatings is usually between 5 and ЗОушп, thinner layers are ineffective and stronger ones tend to break off under stress.

An iesentlich.es feature of the known hart st off be coated hard metals consists in a large difference in hardness between the hard coating and the hard metal body. This difference is usually more than 1000 HY 50 and has the consequence that in the case of stress after the removal of the relatively thin hard material support the wear after it increases due to the action of the layer initially to a slight increase progressively.

This effect is intensified even at high thermal loads, as they are typical in particular for the cutting shaping on the cutting edge. As the temperature increases, the strength of the substrate-type metal decreases, which reduces the supporting effect of the hard-metal base body. In the simultaneously thermally and mechanically stressed area, plastic deformation occurs,

Since the usually hard coating of hard material can not follow these deformations, it ruptures and bursts, ie. h »Removal and removal of the layer are accelerated ·

The heat resistance of the carbide body is determined to a large extent by its binder metal content. To increase the heat resistance, a reduction of the binding metal content is unsuitable, because of this the breaking strength also depends on coated carbide bodies. The binder metal content of the cemented carbide can not be reduced arbitrarily according to the field of application to ensure sufficient tensile strength. "Since toughness losses occur in the majority of known hard coatings, binder metal-rich substrates are often necessary."

In DE-OS 2 435 989 a process is described according to which a coated cemented carbide body with binding metal content is formed in the hard material surface layer by diffusion treatment. The binder metal content is intended to improve the bonding of the hard material layer to the hard metal base body and the ductility of the layer. The presence of the relatively soft binder metal in the hard material layer naturally reduces the wear resistance. Lifting the hard coatings are proposed to increase the wear resistance diffusion treatments, the hard metal body in solid packaging consisting of hard or hard substance-forming, usually solid substances, given and treated according to certain temperature / time regime in flowing reactive or inert gas atmosphere. These diffusion treatments lead, as described in DE-PS 104 41 б and DD-WP 48 642, to solidifications in the surface zone of the hard metal body. In contrast to the hard-coated hard metals, such treated have much lower wear resistance.

To improve the adhesion of Boridschichten on WC-Co-carbide was also proposed in DE-PS 10 92 271, that the coated sintered carbide Pormkörper before applying the Boridüberzuges by annealing above 900 ⁰ C in a Borhiogenid hydrogen Atmosphere is converted on its surface in the Boride of the metals located there.

By means of this pretreatment, the desired higher adhesive strength of the subsequently applied boride layer should occur as a result of the transformation of the substrate surface into the corresponding borides and the associated adaptation of the lattice structure to the lattice structure of the boride layer. Experiments with this procedure have shown, however, that such a pretreatment of WC-Co based cemented carbide alloys results in adverse changes in the surface structure. In addition to cobalt boride (C ^ B), this pretreatment forms tungsten borides, which react immediately after their formation to form double borides, the so-called r-borides of the composition G ° JR-J $ , whose presence leads to severe embrittlement of the cemented carbide body. For carbide inserts made of sintered cemented carbide, which have such a ή- phase, they occur immediately after the beginning of и

the cutting process cutting edge breakouts, which can not prevent the subsequently applied Boridschicht because the substrate body has insufficient strength because of its edge brittleness at this high, stressed point.

In addition, the surface of the pretreated by this method cemented carbide body is also further deteriorated by the fact that in the transformation of the hard material components in the corresponding borides carbon is eliminated, whereby a higher degree of porosity (also called C porosity) is formed, resulting in cross-sectional reductions and thus further loss of pores to Polge has.

Object of the invention

It is the object of the invention to develop a process for the production of diffusion-bonded bilayers on K 10 and E 20 cemented carbide bodies, by which surface layers with a greater wear resistance and adhesion strength can be produced based on the previously known titanium carbide / titanium boride combination ,

Explanation of the essence of the invention

The object of the invention is to improve the reaction and diffusion conditions starting from a titanium carbide-coated cemented carbide body and a reaction atmosphere suitable for the deposition of titanium boride, comprising titanium tetrachloride, boron trichloride and boron trichloride at a temperature between 1150 and 1500 K.

This object is achieved in that the deposition is carried out from a gas mixture containing an excess of 0.1 to 0.5 moles of boron trichloride, based on the stoichiometrically necessary for the formation of the titanium boride layer Bortrichloridmenge.

During the titanium boride deposition process, boron diffuses into the cemented carbide basic body and forms a diffusion zone near the surface. in the cobalt binder metal phase dissolved CopB and on the TiC intermediate layer a TiBp surface layer. The special feature is the borated binder metal phase, in which no harmful η -Boride are incorporated, so that no surface brittleness and C-porosity occur. In fact, the near-surface region acquires one by the partial formation of CopB in the binder metal phase

higher strength, which has a favorable effect on the cutting edge integrity of the cutting edges. In addition, this process sequence results in a better bonding of the TiC intermediate layer to the substrate. The structure of the substrate surface and the intermediate layer permit the conclusion that under these process conditions the TiC interlayer Interlayer takes over a type of control function for the diffusion of the superstoichiometric proportion of boron halide of the reaction atmosphere into the near-surface region of the binder metal phase.

The 3'-diffusion zone produced according to the invention can also be broadened by a thermal after-treatment with simultaneous flattening of the boron concentration gradient.

embodiments

The invention will be explained in more detail below with reference to two exemplary embodiments:

Example 1:

Indexable inserts made of a conventional K 20 cemented carbide were exposed in a reactor at a temperature of 1350 K for 30 minutes to a TiCl 2 -CgHg-argon-tangestoffgemisch. After switching off the CgHg gas stream 3 g of gaseous BCl was introduced into the reaction space, wherein the inflow volume of BCl., - Steam based on the molar reaction ratio to TiCl, in the formation of TiB _2, an excess of 0.15 üol Consequently, 0.1 mol of TiCl ₃ and 0.35 mol of BCl _{3 were} fed per minute.

Subsequently, the reactor was purged with argon and cooled.

The cemented carbide inserts have a thinned double layer consisting of a 8 μm thick boron-free TiC layer and a 2 μm thick TiB 2 layer, as well as an approximately 2 μm thick boron-influenced zone of influence of the substrate.

These indexable inserts were compared with conventional titanium carbide coated indexable inserts and TiC-TiBp coated indexable inserts, with the TiBp layer deposited without BCl., Excess in the gas mixture.

AG / workpiece: longitudinal turning of shafts (smooth cut) Material: GGL 22 HB = 1800 Έ mm " ²

Cutting

speedy. -

speed: v = 150 m min "

Feed: s = 0.5 m U Cutting depth: a = 2 mm

Wear criteria: Free surface wear Б = 0.5 ш Results as service life in minutes:

Conventional TiC-Coated HM-WSP »30 min Conventional TiC / TiB ₂ -coated HM-WSP = 36 min HM-WSP * coated according to the invention 56 min.

Example 2:

Indexable inserts made of a conventional K 20 hard metal were coated as in Example 1. After coating, the temperature was kept at 1350 K for 60 minutes. The insert after this treatment had a closed double layer. It consists of an approximately 8 μm thick boron-free TiC layer and a 2 μm thick Ti3 ₂ cover layer. Below the TiC layer is a ca. 10 μm thick borated zone.

GGL 22 I IB = 1800 Ή τπτη ν = 150 m η S ss 0.5 mm a = 1 τηττι

These indexable inserts were compared with the comparative indexable inserts of Example 1 in a rotary test:

AG / workpiece: facing of 4 piercing bolts

(interrupted cut)

Material:

Cutting speed:

Feed:

Cutting depth:

Wear criterion: Surface wear В я 0,4 mm Results as service life in minutes:

Insert conventionally TiC-coated = 46 min. Indexable insert conv. TiC / TiBg-coated = 56 min. Insert according to the invention coated

and diffusion-treated = 117 min.

The garment layers described in the exemplary embodiments were analyzed by X-ray diffraction, metallography on oblique and cross-section and with the ultraviolet ray microprobe to clarify the phase distribution, the layer thickness and the layer structure.

Claims (1)

invention claim A method of making diffusion bonded bilayers comprised of a titanium carbide interlayer and a titanium boride surface layer on K 10 and K 20 cemented carbide bodies by depositing the titanium boride layer on the titanium carbide coated cemented carbide body from a reaction gas atmosphere containing titanium tetrachloride, hydrogen and boron trichloride. at a temperature between 1150 and 1500 K, characterized in that the deposition takes place from a gas mixture which contains an excess of 0.1-0.5 mol of boron trichloride, based on the boron trichloride amount which is stoichiometrically necessary for forming the titanium boride layer.